I'm adding a new full bath in the basement of a 3 story condo and I don't have where to join an existing vent (the sewer main is under the slab so I have no problem connecting the drainage) so I'l have to add a new vent stack from there to the outside.
So my question is if there is a way to eliminate that the smell should not come out from the vent so I could only come out with the pipe a little and would not have to build a pipe 3 stories high after exiting the building.
Someone told me about putting an upside down u on the way out, Does anyone know about it? Thanks for any help

  • You need to be asking this of your local code inspector since he's the one that will have to approve what you do.
    – topshot
    Commented Sep 18, 2016 at 12:19
  • An air-admittance-valve might work for your application as it only allows air in to the pipe. I don't know if it would be 'code legal' though.
    – brhans
    Commented Sep 18, 2016 at 13:40
  • Stop sending smelly stuff into the vent? Commented Sep 18, 2016 at 20:30

1 Answer 1


This will probably depend on your local code, but it can be done and is done. You have to cap the pipe appropriately, keep it a minimum distance away from windows and doors, and so on.

Here's an existing answer that may help: https://diy.stackexchange.com/a/58659/24137

Another possible option is an AAV, or air-admittance valve. It only lets air into the pipe, not out. So it will allow air into the pipe to perform the same function as an outside vent pipe, while preventing gas pressure from the sewer from pushing smell/toxic fumes into the dwelling. The use of an AAV will very much depend on your local code and your inspector. The one time I did this, the inspector required me to run the AAV 4 feet higher than the line being vented.

AAV's can wear out, so you don't want one closed up inside a wall where you can't access (or even find) it. So where do you locate it? In some cases you can locate them under counter tops. That might work fine for a sink. But you're also talking about venting a bathtub or shower and a toilet. So you're talking about a pretty substantial vent pipe and a large AAV. Definitely talk to your local inspecter first if you consider going this route.

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