I am in the middle of finishing my basement and want to add a sink that will attach to an existing kitchen drain from above. I don't have a way to vent the sink easily unless I use a Air Admittance Valve. The drain will run about 5 feet, make a 90 degree and run another 4 feet. Would the attached diagram work correctly? Anything in blue is the new plumbing.

enter image description here

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    question: isn't the "existing drain from kitchen" already a vented line? Commented Feb 20, 2019 at 19:36
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    In the setup you've drawn, the air admittance valve wouldn't be doing anything that the sink hole itself isn't already doing. The point of vents is to stop moving bodies of water on the sewer side of the trap from sucking the pipe (and trap) dry. Your existing kitchen DWV might already provide enough air as Leo queried above, but if not, put the AAV in the position Isherwood shows in his answer (as long as it's permitted by local code).
    – CactusCake
    Commented Feb 20, 2019 at 20:19

2 Answers 2


The valve needs to be downstream of the trap, basically in the position an actual vent would be.

enter image description here


Also, be sure they're legal where you are. My local inspector forced me to run a new vent line and tie into the existing stack above the upstairs sink drain when I wanted to add a laundry drain.


The diagram installation would reduce the vortex of water draining but it would not be protecting the plumbing fixture trap and it would not be proving a means of venting as defined in the plumbing codes.

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