The 1-1/2” drain from the sink currently runs through the back of the cabinet and down into an interior wall to the basement. The new location will be an outside wall. There is currently no visible drain vent in place. What would be the proper way to vent the line in its new location?

1 Answer 1


There isn't only one proper way. If it's convenient to do so, extend the vent straight upward. If there is attic and roof immediately above then you could make a new roof penetration for the vent and detail with a pipe jack flashing in the usual way. If there's another story of the building above, you could get into that ceiling/floor space and take the vent anywhere - continue upward, route to meet with the existing vent, etc.

If taking the vent up is problematic, route it downward instead. It could be arranged as for an island sink as explained at Family Handyman (they mention two methods: loop as per the image below, or use an air admittance valve).

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  • I decided to go with an AAV. How and where do you recommend I install the valve?
    – Kevin K
    Commented Sep 11, 2019 at 4:17
  • It's probably best to contact your "authority having jurisdiction" (AJH, ie the building inspector) to confirm that AAV is accepted where you are and to ask whether there are requirements as to its position. Absent any guidance from AHJ, I'd suggest it should go in an accessible place such as the sink base cabinet and it should be as high as can be comfortably achieved. Also be aware that an AAV is mechanical and will eventually fail -- it'll either stick closed or fail to seal and would need to be replaced.
    – Greg Hill
    Commented Sep 11, 2019 at 15:13
  • That is good advice AAV’s are not allowed in many locations but they do the job well if placed high placed low they get gummed up and fail sooner.
    – Ed Beal
    Commented Dec 13, 2019 at 14:39

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