What is Wet Venting 90

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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90 thoughts on “What is Wet Venting

    • 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.

  • 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.

  • 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.

  • 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?

  • 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.

  • 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.

  • 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?

  • 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.

  • 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)?

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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?

  • 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.

  • 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).

  • 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?

  • 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.

  • 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.

  • 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.

    • 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.

  • 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.

  • 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.

  • 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.

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  • 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 .

  • 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.

  • 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?

  • 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

  • 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!

  • 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.

    • 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.

  • 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.

  • 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.

  • 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.

  • 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)

  • 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.

  • 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.


  • 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

  • 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