What is Wet Venting 149

Wet venting is a plumbing term and is a method of protecting the trap on a drain pipe on multiple plumbing fixtures.  It is a useful method of venting and can save pipe and fittings, time and money. If you don’t know what venting is or why it’s needed, first read What is Venting?


Wet Vent Definition: A waste pipe that also serves as a vent pipe.

Wet venting is most common in conjunction with toilets and sinks; the drain for the sink is also the vent for the toilet. It can also be used for a variety of other applications but due to the following rules this is the most convenient and common situation to run into.

Wet Venting Rules:

The Ontario code book is written probably by lawyers and is very confusing, so I’ll try to simplify it a bit and include just the most common and relevant parts.

1) A waste pipe may serve as a wet vent provided that,

a) There’s not too much hydraulic load on the wet vent… 1.5″ pipe can not serve as wet vent on a toilet and max 2 fixture units. A 2″ pipe can serve a toilet and a maximum 4 fixture units draining into it.  (Sinks, tubs, showers all have 1.5 fixtures units each). As a general rule, you will just be able to vent 2 fixtures on a toilet wet vent.

b)Toilets must be installed downstream of all other fixtures

c)The wet vented portion of the pipe may not be reduced in size

d)The length of the wet vent is not limited

Practical Examples:

1) Toilet and Sink:

The toilet is vented through the sink drain. The toilet drain should be 3″, the sink drain is 1.5″, the shared sink drain/toilet vent area should be 2″, and the vent going up should be 1.5″. Also note that where the 2″ drain connects to the 3″ at the bottom the fitting should be a y instead of a tee as shown.


2)Toilet, sink and tub (or shower)

Like the previous picture the toilet and sink are wet vented together.  This time the wet vent connects to the vertical leg of the toilet drain which is also good. Also this time we have a tub connected to the wet vent. Here it is shown to have it’s own vent off the drain. If the tub was less than 5ft from the wet vent, however, then you wouldn’t even need to have that extra vent on the tub.  This is a great way to save money on materials as well as saving time.


3) Shower and sink

In this picture it is vented exactly the same as the first example only you will not have the option to tie in the drain to the vertical leg. Also the wet vent area (shared drain and vent section of pipe) can remain 1.5″ if both the sink and shower traps are also 1.5″.



Let me know you have any questions by dropping a line in the comments section. I can also update the blog to better clear confusing points.

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149 thoughts on “What is Wet Venting

  • Casey

    I have a venting size question. I have an older 1960’s bungalow where the vent is 1.25″ copper. It vents the sink in the main bath. It then runs to the main stack and ties in at the very bottom of the stack below the clean out (cast iron). I want to add a washer/dryer in the bathroom. Do I have to increase the vent size to 1.5″ or am I able to leave it at the 1.25″?

  • Pat

    I noticed several people have commented on upstream and downstream. Looking at your drawings the toilet drains toward or down to the sink. To me that puts the toilet upstream of the sink. If the toilet were on the opposite side draining away from the sink it would be downstream. The sink would be higher with a 1/4 inch slope and the toilet would be lower (downstream).

    • mike@jaytechplumbing.com Post author

      Hi Pat. I agree that there seems to be some confusion surrounding “downstream”. To illustrate, I’ll give an example of something incorrect; Say there is 3″ stack running up through the house and the toilet ties into it. You also have a sink that needs to tie in and you install a ty on the same 3″ line below the toilet ty. That would be tying in on the wrong side on the stack as the toilet in not the most downstream fixture anymore. Is this any more clear??

    • mike@jaytechplumbing.com Post author

      A macerating toilet is something entirely different and, in fact, I wouldn’t suggest them at all.

  • Jason

    Hi there. Im currently renovating a second story bathroom. The old bathroom had the tub drain approx 8’ from the 3” waste line and had its own vent 1.5’ from the tub p-trap. The new bathroom design eliminates the tub and goes to a shower where the drain is 3 feet from the waste line. The sink is set as a wet vent for the toilet etc. and the vent out of the house is 2”. My question is do I still need the original bath vent even though we have moved the drain within 5’ of the waste line and venting stack? From my reading and what I see I shouldnt need that other vent anymore. Any info or insight would be great and appreciated. Thank you

    • mike@jaytechplumbing.com Post author

      Hi Jason. This is a great question. It sounds like your shower is stack vented in this case and therefore you do not need to have a separate vent.

  • Lance

    Great article. I’m in the process of renovating our first floor laundry room. Currently the washer drains through a standpipe that is tied to the laundry tub, the only two fixtures. The vent, standpipe and drain are all 1 1/2″, dryer is located on the opposite side of the room. For the reno, we will be stacking the washer and dryer so I will need to move the supply and drain lines. My question is about the venting. The laundry tub will remain in the same spot, but the washer will now be approximately 7′ away. Can I change the drain pipe for the washer to 2″ and run it all the way to the 3″ stack, connect the 1.5″ drain from the laundry tub to the new 2″ drain pipe and and use that connection to wet vent the washer drain through the laundry tub? Thanks.

    • mike@jaytechplumbing.com Post author

      That’s tough to answer without seeing it. It might be a good idea to have a plumber look at it if you’re not sure.
      Thanks for the question though Lance.

  • Greg Brown

    In drawing #2 if the 2″ drain from the tub dropped down into the 3″ main line that is within a 3′ distance, and there is a 2″ wet vent up stream and a 3″ wet vent down stream. Does the tub need its own vent?

  • tim

    This was a very helpful. I am currently finishing my basement and am working closely with my plumber. He has told me that I can vent the basement bathroom through the ceiling and out the side of the house rather than finding a route to the roof. Is this true?

  • Cece

    I am wanting to add a small stand up shower in place of the bathroom sink, I want to connect the shower drain to the toilet drain
    Is this possible PLEASE HELP

  • Rick

    Very nice article Mike! I’m installing a macerating pump toilet in my basement. I purchased this particular system because I could easily tap into the drain at the ceiling of the basement, and I was told that the unit did not require venting “if the drain was a short run.” Well, the instructions beg to differ and I have no access from the basement to the attic nor access to any existing vent. Is it possible that I could run a vent out of the pump, up about 8 feet, and outside to a wall vent? The location is at the back of the house where sump discharge pipes and the dryer vent all are located, so appearance isn’t an issue, but is there a reason why the vent must go through the roof? Or is this something that is acceptable so long as it is up to local code? MANY thanks in advance!

  • Mark

    hello Mike, great information page. i am building a new house that is slab on grade. the plumber has the toilet, shower, double sink, washer and they appear to be vented to a 2 inch pipe that comes out of cement then is reduced to 1.5 inch up the wall with a run of about 35 feet in the attic area to a 3 inch vent pipe that runs up through the roof. Can that vemt line handle all those fixtures. They are in relativley close proximity to each other (cant be sure if runs are 5 feet or less for wet drain), but still makes me nervous. Also the vent line that runs in the attic is 1.5 inch does not appear to slope but has dips in it where condensation can gather. am i in trouble.


    • mike@jaytechplumbing.com Post author

      A 1.5″ pipe is likely a sufficient pipe to handle the load but you should make sure that it doesn’t trap water anyway.
      Thanks for the question.

  • Aaron

    House was built in the 40s. The toilet, sink, and shower all use the same wet vent. The pipe starts with the tub then hits the stack, then continues to the sink, then the toilet, and then to the city sewer. Water is getting sucked out of the sink trap and nasty smells come up te sink sometimes. Whats the best way to repair this? An AAV for the sink?

  • William Liu

    Hello JayTech,

    On your 2nd Example, with the toilet sink and tub; wouldn’t the toilet be considered upstream of the wet vent, thus creating a problem with siphoning?

    In 2012 UPC, 908.1, Vertical Wet Venting. In the vertical wet vent, only trap arms are connected to the wet vent, not waste branches. From the look of this picture, isn’t the WC connected to the wet vent.

    This would be corrected if the wet vent connection was on top of the toilet correct?

  • Bruno Langemann

    I am adding a 3 piece bath and am wondering if the basin ( continuously vented )and sized 2″ at the trap arm. Can it also vent a shower drain approx 5′ 8″ away and this 2″ line tie into a 3″ drain downstream of a WC.

  • Ben


    I’m doing a basement reno, and trying to figure out if my laundry room needs a vent.

    What I think makes my situation a bit different is my laundry tub (without P-trap) drains into a sump pit (uncovered), the waste is then pumped out to an old existing French drain in the yard. It’s an old house and I’m assuming this was common in that era. I should mention my washing machine drains into the laundry tub. Currently everything seems to drain well, and no sewer gas becuase it’s an independant system.

    What I plan to do is drain the washing machine into a recessed water box (to clean up the look), which would drain into the sump pit. And have the laundry tub drain (the laundry tub located closer to the sump pit) drain into the line connecting the washing machine drain and the sump pit.

    1)Since the laundry tub and washing machine are the only appliances draining into an uncovered pit, will they need a vent?
    2)Would this need a vent if the pit was covered?
    3)And should any of these appliances have a P-trap, and why?

    Thank you very much!

    • Mike

      Hi Ben.
      Those pits aren’t legal any more. I can’t comment on how to vent a pit that’s potentially draining contaminants into the ground.
      The best would be to have a sewage pit or laundry pump and drain it into the plumbing system.

      Thanks for the question though.

  • Brad


    I am completing a shower stall update on my parents bathroom for them. Existing shower is plumbed with 1-1/2” ABS from shower drain to the stack. I am assuming it is tied into existing bath tub or vanity sinks on its path back to the main stack.

    That said, the new shower stall will have (1) 10” railhead and (1) standard wall mounted hand wand. The shower stall is 36” x 60” prefabricated acrylic base. My question is how to tackle the 1.5” existing trap and sanitary line? I cannot replace as I would likely have to tear up the entire floor and re-plumb all fixtures.

    The shower base came with 2” shower drain.(Oaty, No Caulk Drain) What are my options? Can/should I reduce the 2” drain to 1.5” before or after the trap? Should I see if I can get a 1.5” shower drain ( I haven’t had any luck in the last day sourcing one)? I understand a reduction amounts to an impedance for draining and is why I assumed the best option would be to stick with 1.5”. Just not sure how the drain would perform if both railhead and hand wand were used at the same time..then again, shower heads are mostly low flow and more efficient than they were many years ago.

    I know 2” all the way through is preferable but I do not have the option to re-plumb everything. Can you provide any clarity here?

    • Mike

      Hi Brad.

      This is actually a very common scenario and what everyone does (and is totally fine) is bush it down to 1.5″ right at the shower base.
      Thanks for the question.

      God bless.

  • Ron

    The attached sketch shows proposed venting for back to back bathrooms. Sink 2c did not have a vent, WC2A exceeds 6′, WC2B is new and exceeds 6′, Sink 2A and 2B are new, SH2 is existing, Tub is new. 3″ stack needs to be offset 15″.
    The first fl is what I was able to trace and not sure if this is correctly piped for the drain and vent.


  • Roger Spotswood

    I have a 2″ shower drain 6 feet long connecting to a 3″ extension running an another 6 feet to a 2 inch wet vent with two sinks (1.25″ traps on each) with the sinks connected to the 2 inch vertical drain/vent in a double sanitary T. Is the shower adequately vented? I can supply a pdf digram if necessary.

  • jeff

    Thank you for this article! This has been very helpful. I was wondering if I can tie into the main cast iron vent in my house for a half bath upstairs. I noticed all your diagrams have the sink going into the wet vent but not a toilet. Is that okay?

    • Mike

      Hi Adam. Your link didn’t work but if the picture is the same as the comment below it, then it’s done correctly, and if the inspector passed it, then for sure it’s done well.

  • Lina Thai

    Hi im having my nail salon remodeled and the plumber wants to add vents to all 10 of my pedicure chairs. I dont believe it is necessary but I dont know how to explain it to him.

    • Simon Parry

      First of all, I’m not a trained plumber, but I’m in the middle of a project which involves venting and I have learned that “the code” allows for no more than 2 items to be connected to the same drain which is vented with the same single vent pipe. So if you have 10 items (10 pedicure stations each with drain and P trap) then I would have thought you can double them, with two stations being served by one vent (providing it’s the right size / diameter. 1.5″ should be adequate. The vent simply ensures that when a large body of water (in a foot bath for example) is released, the suction doesn’t pull-out all the water in your P trap. If this happens you are then open to some rather nasty sewer smells which will not go down well with your clients. Ask your plumber why he thinks 5 vents – one for every 2 pedicure stations – won’t be sufficient and you can always ask him to call your local ‘code people’ for their perspective – but watch-out, they may want you to get a permit!!

    • Mike

      Hello Lina. Anything that has water lines and a drain will need to be trapped and vented. The plumber is correct and things need to be vented properly. These rules are put in place for your own good… without them you’ll be getting sewer gases into your salon.

  • kenji sasaki

    Hi Mike, thanks for the explanations and the forum! I have a bathroom remodel with lavatory, shower, and WC, but walls are closed/tiled.
    Right now, all three are in a line like: vented lav, WC, shower, then soil stack.
    Can these be correctly connected without an additional vent installed?
    I cannot use a 2-to-3 heel-in from the sink to WC line, right? it has to be a horizontal-connected sanitary T?
    thanks again!

    • Mike

      Hi Kenji,
      More than likely you’ll need to separately vent something. By the sounds of it, I would wet vent the toilet and sink together and dry vent the shower.
      All the best

  • Simon Parry

    I want to connect a shower drain to a toilet drain. (I am pretty sure the toilet is already vented according to Ontario Plumbing codes of the early 90’s which is when this house was built.)
    The shower drain will have a P trap on it and the drain pipe will run across (under the concrete floor) to link up with the waste pipe from the toilet. It sounds as if this connection cannot be downstream from the toilet. If this is the case it will have to connect into the toilet (soil) pipe into the 90 degree curved pipe under the toilet. (I’ve never seen such fitting in Home Depot.)

    Your advice in this will be most helpful.
    Thanks very much.

    • Mike

      Hey Simon,
      There might be a bit of confusion there, but you can tie into the horizontal toilet drain with a ‘y’ fitting. Just make sure that your shower is still vented.
      Thanks for the question and good luck with your project.

  • Rick Deis

    Great info Jay. Thanks for sharing. 1. a) states ” a) There’s not too much hydraulic load on the wet vent… 1.5″ pipe can not serve as wet vent on a toilet and max 2 fixture units. ” I trust you meant 1.5″ pipe “can” serve instead of “can not” ?
    After years of the basement toilet making gurgling sounds and overflowing a couple of times I’ve torn the entire bathroom out and plan on redoing everything. I’ve discovered a couple of things which I believe have caused my problems. I’ll try and give you an idea of my setup prior to asking my questions.
    Our bungalow is L shaped with main stack on one segment of the L and the basement plumbing/sewer exit on the extreme end of the other segment. All the main floor sewer lines flow into a 3″ horizontal pipe and then vertically drop straight down into the basement floor in line with the bsmt bathroom wall and then exits the house beneath the opposite bthrm wall (outside wall). There is a cleanout on the bottom of the vertical (soil stack) and a 1.5″ drain pipe coming from a laundry sink ptrap/standpipe/ptrap combination .
    The 7′ x 7′ bsmt bathroom plumbing consists of a toilet 15″ off the wall and directly in line with the under slab sewer (13.5″ from left concrete wall) next is the sink plumbing which consists of 1.5″ drain /1.25″ Vent about 4″ off the left concrete wall. This 1.25″ vent eventually ends up as a 2″ vent exiting the roof. I’m not sure if the main floor laundry ties into this vent. Next is a 2″/1.5″ bathtub drain (Originally intended for shower as it is 20″ off the left concrete wall and 18″ off the sewer exit concrete wall.
    1./ Inadequate venting? Will the sink venting serve to wet vent the shower drain ?
    2./ Toilet T directly into sewer is a no no?
    3./ Can the soil stack/waste stack coming from the main floor be used for the bsmt plumbing venting?
    Hears what I am planning; can you comment on my plan or any easier way?
    a) Install shower instead of bathtub.
    b) Remover the laundry sink/standpipe plumbing and somehow use it for my water softener drain(previously drained into sink). Maybe like a the hookup for a dishwasher drain?
    c) Relocate the toilet and tie in a vent from it (in the ceiling) into the 1.25″ sink vent

    Rick D

    • Mike

      Hi Rick,

      Question 1:
      A toilet always needs a 2″ wet vent. Only when it’s dry vented can it be 1.5″

      Question 2:

      I feel you should be getting a plumber in to take a look at this one Rick. There’s too much going on to communicate over a blog post. Thanks for the question anyway.


      • Rick Deis

        Thanks for the info Mike. Unfortunately my rural location makes even getting a quote somewhat expensive. I’m better served finding out exactly what I need so I can get several quotes.
        If you could just clarify one thing for me and that’s in regards to determining what is the effective vent size? In my case where the basement sink vent goes from 1.5″ and then reduces to 1.25″ in the wall above the flood line and then continues to the attic where it ties into a 1.5″ kitchen sink vent. That 1.5″ pipe then ties into the 2″ main floor laundry vent which terminates through and above the roof. What size is basement sink vent?



          • Rick Deis

            Thanks Mike but there appears to be a bit of a misunderstanding. The question was “what is the effective vent size” Is it the size that exits the waste pipe( 1.5″) or is it the smallest size it gets reduced to along its path (1.25″) or is it the size that exits through the roof (2″) ? Seems to me somewhat pointless to have reduced it to 1.25 as that size is actually more expensive than 1.5″ or 2″. Plumbing was done sometime after 1970 and prior to 2002 when we purchased the house. I expect it was early 70’s as its all copper. If you choose to ignore I understand.



          • Mike

            The appropriate vent size is dependant on the load serving it at any given point in the system. The further down you get and the more fixtures are tying in and adding load, the bigger the vent size needs to be. Getting a plumber in to determine things for you is probably a good idea.

    • Mike

      Sorry Luis but that case won’t work out. Try dry venting the tub or shower and wet venting the other two with a vanity sink or something. That’s usually the best case scenario.
      All the best!

  • Dennis Patterson

    Hi, thanks for the great articles. I’ve read a lot of the code, and done a lot of research but I’m not sure if my plan will meet code and I’m hoping you can help me out. Part of the trouble is reading too much online I’m sure. I’m converting the basement to an apartment and therefore have to add laundry and a kitchen sink. I have a basement washroom(toilet, sink, shower) and a main floor laundry on an aux vent at the back of the house. The main stack is about the middle of the house. Toilet has a 2″ vent, can I add a clothes washer in the basement to this 2″ toilet vent? Can I add a kitchen sink in the basement onto the main stack (3″ stack add a 3x3x2″ fitting for the drain and vent it out the back aux vent ( about 6 m away)? Hope I’ve left enough detail for you to answer.

    • Mike

      Hey Dennis. I believe you can tie in your fixtures to the drains that you wanted as long as you still separately vent them and tie those vents into existing dry vents. Let me know if that makes sense to you.

      Mike – Jaytech Plumbing

  • Andrew

    I’m putting in a basement bathroom. All units; sink, toilet and shower, are draining into a sewer pump pit in which I must install a pump that is supposed to have a 2″ vent. I’m wondering if I can ty into an existing 2″ drain pipe as the vent for this pump pit… The 2″ drain pipe services only the kitchen sink. Can you help me answer this question?

    • Mike

      Hey Andrew. According to code you are supposed to tie it into a dry vent that is the same or greater size. More than likely you’ll need to tie it in at the attic if there wasn’t a vent previously provided for this purpose. All the best man.

      Mike – Jaytech Plumbing

  • Robyn

    I’m an amateur DIY plumber. Just to make sure. The wet vent size servicing the sink and the toilet can be 1.5 inches, or is it 2 inches. Someplace I read said it has to be 3 inches??? Somewhere along the line, the shower is vented too. My husband re-routed the shower drain for curbless wheelchair and I’m not sure how he did the vent for the shower drain. Robyn

    • Mike

      Hi Robyn.
      The combined sink drain/ toilet vent part of the pipe needs to be a 2″ pipe. The toilet drain is 3″ and the dry vent part is 1.5″.

      Thanks for the question.


  • Jason

    I am moving my washer to a shared wall with a bathroom. All bathhroom fixtures have their own vent. (Sink 1.5″, tub 1.5″ and toilet 2″) i want to cut the laundry tub drain into the tub vent and the 2″ washing drain into the toilet vent. Can i do this? If not, can I vent the washer into the sink vent and drain it into the toilet vent? It is a single story.thank you for your time.

    • mike@jaytechplumbing.com Post author

      I would probably wet vent the washer and laundry tub together, put the drain into a drain below the floor and tie the vent into one of the existing vents in that wall.

      • Daniel

        I have a similar situation as Jason. Trying to tie in a washer drain into a 2″ toilet vent. This is located on a slab so going below the concrete is not an option.

  • Mike Hoffman

    In your first example, it seems to me you are violating rule 1b, toilets must be downstream of other fixtures. (Or maybe “downstream” from a vertical sense)

  • Steve

    I am a little confused by the statement “Toilets must be installed downstream of all other fixtures” In the example 1, it sure looks like the toilet is upstream of the sink.

    • mike@jaytechplumbing.com Post author

      Try to imagine the toilet drains above the ty on the sink drain in figure 1. That would be upstream.

  • Henry

    I’m wet venting a toilet and tub. If tub is more than five foot can I run 2 inch pipe within 5 foot of tub then go to hook up sink? There is no maximum distance for the sink drain right? So as long as I put my 2 by inch and half y within 5 foot of tub does it matter length of two inch pipe from the y to the sink drain coming down thru floor?

    • mike@jaytechplumbing.com Post author

      Great question Henry. You are absolutely correct. The section between the tub y and the sink can be as long as needed.

  • Mohiuddin

    Thank you very much for the diagram very insightful, but I still have one question, if I were doing the second scenario in the basement All three fixtures, in what pipe would I vent? Can I do it in the same drain stack ( as some people have suggested) by putting a tee up in the middle of the stack, if this were so would the other waste coming down this drain not also get into the vent pipes? Really appreciate your answer. Thank you very much.

    • mike@jaytechplumbing.com Post author

      The vent needs to go off the sink drain to prevent the sink from being s-trapped and therefore potentially siphoning out and sewer gas escaping. Thanks for the good question.

    • mike@jaytechplumbing.com Post author

      There’s a way to do multistory wet vent properly but the right conditions need to be met. The simplest thing for you would be to wet vent together fixtures from the same story.

  • Edray

    Hi Again,

    I did mean to say wet vent and not in-line. The main stack is a waste stack as the bathroom upstairs is tied into it.


    • mike@jaytechplumbing.com Post author

      Hi edray. You can drain the sewage into it, but the vent must be tied in above the flood level rim of the highest fixture.

  • Edray

    Hi there,

    I want to install a sink in my basement where there is no rough in. There is a waist stack about 5 feet from the sink location. Can I hook directly into that stack for waste drainage as well as an in-line vent?

    Thank you!

  • sam

    my question:
    can a vent pipe be installed before the p-trap on a shower?
    I am being told by one plumber that it is ok and one plumber that it is not and will siphon the trap.
    from the show pan – PVC 2 inch drain runs about 18″ (maybe less) to a T – the vertical is a 1 1/2 in vent (that runs into the attic) – the horizontal (for the water) runs a few inches drops a couple inches runs about 2 feet on level to the p- trap which then runs about 2 feet and drops to tie into the 4″ soil pipe that angles into the basement slab.
    do I need to rebuild it all?

    • mike@jaytechplumbing.com Post author

      That’s done incorrectly and the vent is basically useless as is. If it starts causing you issues, it should be fixed properly.
      Thanks Sam

  • Sheldon Carter

    I have a double kitchen sink under a window with an admittance vent. This arrangement is not working. It still drains slowly and burps sewer gas. The vent is opening and closing correctly. The top of the vent is located just above the sink bottom. Is this location a problem? Any other ideas how to make this work correcly?

  • Nick

    Hi, I have a pretty unique problem, I have an extension on my home over a crawl space. This area has a 1/2 bath , toilet on sink , with the sink being downstream of toilet. The vent pipe is on the interior wall of this room located another 3 feet on the downstream path. None of the plumbing is on the outside wall , everything is ran up from the crawl space , should I put the vent pipe such that it top enters the 3″ toilet drain pipe between the sink and toilet ?
    Your advise would be greatly appreciated,
    Thank you,

    • mike@jaytechplumbing.com Post author

      Hey Nick, I’m having a tough time grasping the situation there. A picture says a thousand words however; try to emulate one of the scenarios depicted on the page.
      Sorry I couldn’t help further.

  • James Wickes

    My ensuite has a corner tub with a toilet beside it on the right side. On the left side of the tub is the shower. there was a sink on the left side of the shower. We are moving the old sink and installing a double cabinet and 2 sinks across from the shower. Where the old sink was is the vent pipe in the wall which the old sink drained into. Can I drain the 2 new sinks into the vent pipe were the old one was .

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  • John Acosta

    I have a Santiflo pump up system. I would like to know if I can connect to the 1 1/2″ waste line(with Y)(which is vented) & also vent into the same 1 1/2″ waste line 12″ back from where the 3/4″ santiflo discharge line enters. The waste line is above the the saniflo unit.
    I was placing the entries of vent & waste from the top of the 1 1/2″ waste line.
    I assume this is considered a wet vent.

    • mike@jaytechplumbing.com Post author

      Hey John, that’s a unique situation where technically you have a toilet on your saniflow and therefore the wet vent should be a 2″ pipe but the discharge is actually much smaller. Its probably ok but the only worry I would have is if the the 1.5″ pipe plugs up then the saniflow has nowhere to pump. In this case I would recommend just using your best discretion.

  • vaibhav sharma


    please clear me
    where the 2″ drain connects to the 3″ at the bottom the fitting should be a y instead of a tee but why we use y instead of a Tea and how we will make selection of y and T fittings in different cases of plumbing.

    • mike@jaytechplumbing.com Post author

      Think of it like directing the water which way to run. If it’s just a vent (no water running through) then you may use a ty, but with water use a y.
      Thanks for the question.

  • Richard Bair

    I built a house in Hawaii as owner/builder. I also plumbed the house. At the time I plumbed it, Sure-Vent by Oakley were code. Now in the process of getting an “as built” permit, I find the code changed. Do I have the option to wet vent the 3 sites? Kitchen sink. Washer. & Lab sink.

    • mike@jaytechplumbing.com Post author

      Hey Richard. That all depends on how the system is plumbed in. Unfortunately I can’t give you an answer without further information. Sorry.

    • mike@jaytechplumbing.com Post author

      Should be ok but look into the local codes on that one. Over here, the code changed recently that you need to run a 2″ trap on laundries… just something to think about.

  • Tracey Taverna

    Would the above apply to using a “wet vent” connecting a kitchen sink to a prep sink in an island, or would you recommend using an individual vent for the island sink?

    Many Thanks,

    • mike@jaytechplumbing.com Post author

      Hey Tracey.
      Venting an island sink is a bit tricky and possibly a good idea for another blog post. The basic idea though is to have the trap under the floor instead of the vanity and have your vent tie off still 5ft away max. If your wet vent ties in there, perfect, otherwise it’ll have to be individually vented.
      I hope that makes sense.

  • John

    Two story house-no bsmt
    Stack in lower level plumbing wall lines up perfectly with upper level toilet and has no fixtures on the lower level. I want to wet vent upper level toilet with vanity with a 3x3x2″ t-y in joist space. Inspector says vertical leg cannot exceed 1m.
    Looking at the code my interpretation is its 1m vertical before a vent is required.
    Your opinion?

    • mike@jaytechplumbing.com Post author

      My opinion is that you will not win an argument with the plumbing inspector… he is always right lol.

  • N

    Hello Mike,

    I have a 4″ vent stack attaching to sewage lateral in the basement and going vertically from the basement through the main floor, 2nd floor, and attic through the roof.

    There are four four piece bathrooms in the exact same area of the floor plan — one per floor including the basement and attic.

    All of the plumbing fixtures in the bathrooms are within 6′ of the main stack and I am wondering which, if any, of the fixtures / bathrooms can be wet vented by draining directly into main stack through a wye?

    In all cases the toilets are wall hung and are located less than a foot from the stack so drain directly into it. Can I wet vent all of the attic fixtures by tieing them directly into the stack? Can I wet vent any of the other toilets being that they are only inches from the 4″ soil pipe?

    I was considering running an additional 2″ vent directly adjacent to the 4″ stack to vent the lavs and tub/showers but trying to wet vent all of the toilets by tieing directly to the main stack.

    Also, how near to the trap does the vent have to be? Can a 2″ line draining into a main stack be vented say 5′ away from the p trap or does it have to be closer?

    Thanks so much for considering these questions!

    • mike@jaytechplumbing.com Post author

      Wow, that is some unusual plumbing going on in your house. I’ve very rarely seen a wall hung toilet in a residential house and you have 4 of them, haha. With this situation it would be best to come and take a look at the project to decide the best course of action and for sure would get a professional to tackle it. Thank you for the inquiry and all the best.

  • ron

    Someone asked this question earlier (John Sept 21, 2013) but you didn’t actually answer his question. You state that toilets must be downstream of vents. You wrote:

    b)Toilets must be installed downstream of all other fixtures

    However in your diagrams the toilets are all UPSTREAM. >????????????

    • mike@jaytechplumbing.com Post author

      Ok, thanks Ron, I think I see the confusion… in the diagram below, imagine the toilet and the sink are switched. It would be illegal because the toilet needs to be the fixture further down on the wet vented pipe. Is that making any more sense?

  • Noel

    Hi Mike. VERY informative article. 3 questions, if you don’t mind:

    1. What is the rationale behind the 5′ distance?
    2. What is the maximum distances between the vertical vents, ie not the distance between the fixture and the vent, which must be less than 5′, but the distance between the various vertical vents themselves.
    3. I’ve been looking at the Ontario Building Code S7 for an hour and cannot find the subsection that specifies the minimum 5′ distance (which I assume is 1200mm as it’s all in metric). Do you know which one it is?

    Thanks so much,


    • mike@jaytechplumbing.com Post author

      The 5′ rule came into effect because a lav only needs to have a 1.25″ trap/pipe and has to slope at 1/4″ per foot. So after 5′ it’s sloping more than the diameter of the pipe and is prone to siphon, leaving the trap dry and the smell escaping. As for the vent, you can connect as far as you want (within reason).

  • Greg

    Hello, Mike.

    Thanks for explaining things in a clear manner.

    I had a continuous 3″ vent stack that served as the the vent for the house, and the soil stack for the main upstairs toilet, bath and lav. It ran down through a supporting wall which I replaced with a beam – hence the soil stack/vent had to be cut.

    I still want to tie in to the remaining vent stack as the rest of the house uses it, but I am routing a new soil stack for the toilet, bath and lav., and wet venting the whole works in an identical manner to the figure 2 above.

    My question is how do I tie the (new) 2″ wet vent into the existing vent stack, please? Do I put a 90 elbow, then reduce it to 2″ to tie into it? Do I put a 3″x3″x2″ tee and then glue a 3″ cap to the bottom of the stack below the tee? And how high should I tie the 2″ line into the stack?

    Thanks again for sharing your expertise so generously.


    • mike@jaytechplumbing.com Post author

      I’m not too sure why you want to reduce it if you still have a toilet running into. I’m sorry for not quite understanding your situation.

  • Guimier

    Hello Mike. I presently have the toilet/sink setup you’re showing in figure 1. I am in the process of adding a shower. My easiest option is to connect the shower drain into the toilet drain with a y connector located 3 feet downstreeam from where the sink Y connector to the toilet drain is. I cannot connect a vent pipe for the shower to the vent pipe for the sink. Will the wet vent through the sink be ok to also vent the shower drain?

  • Dan Reyburn

    Can you tie in a kitchenette sink to a tub waste line through the overflow / lever stopper pipe? The trap under the tub is too close to the joining of the tub drain line to tie in there.

    • mike@jaytechplumbing.com Post author

      Sorry Dan, it’s not legal nor is it a very good idea. You’re best to find a proper way of doing it.

  • sanat

    Hi, first i wanna say that i appreciate your hard work. Really helpful.my concern is the 3rd diagram.it looks like the lav drain which is actually wet venting the shower has the shower draining into it whereas it should be lav draining into the shower fixture drain,downstream of the shower trap for the lav drain acting as a wet vent….

    • mike@jaytechplumbing.com Post author

      It’s really the same difference actually… Connect the two together with a y fitting. Either way the sink drains and the shower vents.

  • DC

    To properly vent a septic pumpout in the basement, I understand I’ll need to use 2″ pipe. I will run this pipe to the attic vent before tying it into the existing 3″ stack from the main floor plumbing. Is it necessary or advisable to make that horizontal connecting portion (less than 5 feet) to be on an upward angle (using 45 degee connectors) to accommodate possible frost build up and subsequent melting so that any melt water will drain back down the 2″ pipe? Also, can I wye in a basement laundry tub to this same 2″ pipe and use it as a wet vent?

    • mike@jaytechplumbing.com Post author

      No need to slope it, frost won’t be an issue. As far as the wet vented laundry is concerned, it’s technically not permitted here in Ontario code but it should work fine. You may need to check you’ll local code on that.

  • Joe

    I am in the process of finishing my basement bathroom. I have a slab floor and live in Colorado. I need to cut out a chunk of concrete so i can move the plumbing around. The builder was not very kind on leaving them in the correct spot.
    Ho would i go about venting these pipes. do i have to go out the side of the house or can you vent 55\\\” up the wall in the framing studs?? need help on this. I have done sum plumbing but never a finish basement.

    • mike@jaytechplumbing.com Post author

      Hey Joe. You can put the vent up in the outside wall. No need to bring it out the side… as long as it protrudes through the roof somewhere.

  • Paul

    Mike…..Installing a basement bathroom with a sewage ejector. Running 3″ pvc straight to toilet (about a 5′ run). Between the pump and toilet I’m branching off with a 3×2 wye to pick up the shower. Right before the shower trap will be a 2″ sanitary Tee which will vent the shower and wet vent the toilet. I’m planning on running the 2″ up into the wall and then reduce down to 1 1/2″ to pick up and existing vent. Does this sound ok. The sink will be tied into the 3″ trunk with a 3×1 1/2 sanitary tee right after the pump. The sink has its own vent which I plan on tieing the shower into in the ceiling. The ejector needs to have its own vent up threw the roof. Would tieing into my stack which is 4″ with a 4×2 tee just before it exits the roof be sufficient. I would hate to cut another hole in the roof.

    • mike@jaytechplumbing.com Post author

      Just as you described sounds like it’ll work fine and yes by all means tie in your vent before it exits the roof. The less penetrations the better. Nice work Paul.

  • Max

    Hi. Great information here! I have a single story house with plans to add a bedroom and bathroom in the attic. The new bathroom will be located directly above an existing bathroom. There is a 3″ pvc pipe in the attic that vents that bathroom and the utility room. Is it acceptable to tie into that 3″ vent for waste? Or, should I run a separate waste line down into the main trunk line (which would involve chipping much concrete to get under the slab)?

  • chris

    If I am installing a 1/2 bath (sink/toilet) that is 20′ from the main stack what are my options for venting?

    I assume that I would do a 2″ wet vent all the way up to the roof. My plumber is saying that we can go 2″ all the way up to the attic and then tie into the main stack up there for a vent outlet. Seems odd to do it that way, is this ok?

    • mike@jaytechplumbing.com Post author

      There isn’t any problem with tying vents together in the attic. I prefer this rather than making multiple protrusions through the roof.

  • Austin

    Hi mike,

    I ran across this page when searching for information for a similar project. I have a 3rd story loft in my home and I would like to add a small bar sink up there. I had ordered the rough ins from the builder but they missed it and I didnt make a big deal in time. The location I want it at is directly above the main bathroom. The wall I want it on has a side attic on the other side that I can access through a 2nd floor trapdoor almost exactly behind the bathroom. I am certain that the vent for that bathroom is going right past the spot I want to rough in. I would be tying in approx 11 to 12 ft above the toilet is this feasible? Worst case scenario, I can probably run another vent up to the roof , but id rather avoid that if possible. I havent looked up there yet, but I know the toilet vent atleast goes straight up. Now whether hot or cold water is accessible will probably be the sticking point….

    • mike@jaytechplumbing.com Post author

      It shouldn’t be a problem to connect the vents together but depending on finished walls and access you’ll likely have a harder time finding a drain to tie in your bar sink too. Can you get the drain to the other bathroom?

  • John

    I may be understanding the first diagram incorrectly but, isn\\’t the layout incorrect according to the wet venting rules you laid out. To me it appears that the toilet is upstream of the sink.

    • mike@jaytechplumbing.com Post author

      Thanks for the question John. If you look carefully you’ll notice that the drain from the sink also serves as a vent for the toilet. This is actually why its called a wet vent.

  • Mark

    HI,, installing a three piece bathroom, plus picking up a washer machine and floor drain in my basement. I need to install a vertical vent from the roof,. All this will be going to Sewage Basin, than pump up to feed to the septic system. The question is how It would be easier for me to bring the vent down to the ceiling of the basement, than travel 10 ft 90 * than another 10ft horizontal then down the wall to the floor,,, would this be ok, . I will be installing 3 inch ABS from the toilet to the sewage basin, with everything else Y’ing into this.

    • mike@jaytechplumbing.com Post author

      If I understand correctly your vent from the roof seems ok, but just make sure everything in the bathroom is vented correctly and then tied into that vent. As a note, the sewage pit needs a 2″ vent.

  • conrad

    where should the vent go for the toilet if the toilet is more than 4ft away from main drain, front or back and how far from the toilet should the vent be?

  • Brad

    I recently put in a new bathroom and tied into the old outside vent stack, it flushes slow and will back up after the shower runs about five minutes. I can send pics if you can advise, thanks. I tied all in and put a very good vent cap on the upper side of the farthest unit, the sink. All runs together. Sink went to 2 inch in wall and has breather cover on the wall so its getting air i guess

    • mike@jaytechplumbing.com Post author

      If things are vented well and your drain backs up after 5 minutes of use, then I would assume that your old drain is a bit plugged. You should get a plumber to snake it out or rent one from the local tool rental store. All the best Brad.

  • Jamie

    Hi! What a great site! Thanks for your help. I’m looking at your 3rd example of wet venting. I am planning a 3piece basement bathroom, with drainage tying into main waste drain (3″ cast iron), and the option of venting tying into 1.5″ vertical vent which currently vents laundry sink.

    Question: I have a vanity sink upstairs, with a drain that currently runs across the basement ceiling, into the main stack drain at head height. I am wondering if I can cut and reroute this upstairs sink drain, down the basement wall and under the floor, (using 2 inch abs) and tying the basement shower into it as wet vent/drain before it ties into main drain. The 3rd wet vent example given in your ‘wet venting’ discussion is exactly the layout, except that the wet vent/sink drain would have several turns in it, on it’s way down. (The basement toilet and sink would tie into the main drain separately, and each vented with a horizontal line to the laundry vent)

    Alternatively, I’ve thought about leaving the sink drain separate, and venting the shower separately with a horizontal around the walls to the laundry tub vent, but this seems a waste of material if the first example is acceptable.

    • mike@jaytechplumbing.com Post author

      There may be another option for you Jamie and I’ll do my best to picture it here… All three fixtures for your basement bathroom can be vented through one vent: 3″ toilet drain has a 2″ y fitting to pick up the sink drain which continues up as your vent after the sink (Much like example 1 but there will be some horizontal pipe underground on the 2″). As for your shower, if you tie it into your 2″ underground within 5ft of the trap then it doesn’t need a separate vent. This would save you a lot of work. Let me know if that makes any sense to you.

    • mike@jaytechplumbing.com Post author

      Hey Hank. Sorry if it was confusing, but it says that a 1.5″ can not serve as a wet vent for a toilet. So you are correct to say that it should be 2″. Thanks.