I'm replacing my double kitchen sink and replacing an S trap with a P trap. There is no vent nearby that I can tie into easily, so I'm going with an under sink AAV. Issue is, I don't have much space between the current s trap and where the drain ties into (through the floor):

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Here are some ideas I had to fit a P trap and AAV on here:

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I ran out of parts, but my idea is to use 90 degree elbows to circle back to the drain in the floor, and use another 90 pointed down or a j bend to get it into the drain.

Would that solution work without the risk of code violations?

Or would this configuration work better? enter image description here

Thank you for the advice!

  • You don't want the two sink drains to compete with each other for the exit point. Typically you have a straight piece coming down from one of the sinks and the other joins that down piece. Sep 24, 2019 at 17:28
  • There's a partition at the top of the tee where both sides of the sink join together, so even if there was full drainage from both at the same time, they shouldn't compete
    – peter
    Sep 24, 2019 at 17:37
  • That plumbing is bad. Should look like: secure.img1-fg.wfcdn.com/im/42040126/resize-h600%5Ecompr-r85/… Sep 24, 2019 at 21:16
  • Can you get access to the plumbing below the floor? Sep 24, 2019 at 23:57
  • Not easily. It's a 200 year old house, and there's an abandoned cistern directly below this drain
    – peter
    Sep 25, 2019 at 3:03

2 Answers 2


In your 4th photo you have the sanitary tee oriented improperly ( horizontally instead of vertically ) but in your 6th photo you have it correct ( but you have an incorrect fitting on the top ).

The sanitary tee will sit on the straight drain pipe going down through the bottom of the cabinet, it will accept the pipe coming from the trap. Depending on space you may not need to take such a circuitous route to get the trap outlet into the san tee. ( Meaning you may not need the 90 elbow going into the san tee, the trap swivels and you can cut the pipes to try and make a straight run to the san tee )

For the AAV you can come off the top of the san tee and then 90 over to the side of the cabinet and then 90 up so the AAV can go up between the side or back of the bowl and the cabinet ( anywhere there is room for it. )

It needs to be a high as possible. Put a threaded connection just after the 90 that turns up so you can pull it out if you need to change or service the AAV in the future.

  • Yeah, I have the santee on upside down. I have female 1.5" threads on top for the AAV. The AAV will fit higher without the 90s. Do I need them for any other reason, or are you saying I can use them to position the AAV if needed? Thanks, this is helpful. I wasn't sure if the p trap arm could be rotated the way I did, or if that would cause problems.
    – peter
    Sep 24, 2019 at 17:37
  • You can not just put the AAV directly on the san tee with the threaded connection the way you have it shown. It is to low ! You need the AAV to be higher then the drain bell on the bottom of the sink bowl, That means it need to up between the bowl and the side of the cabinet. You need the 90's to get it over so you can accomplish that. That means it is in a tight place and unscrewing it up there is a pain in the neck. the threaded connection lower then the bottom of the bowl allows you to get it out if needed. The san tee is not upside down in your 6th photo.
    – Alaska Man
    Sep 24, 2019 at 17:56
  • The side inlet of the san tee with have sweep or curve as goes in. The sweep should go/point down so the liquid will flow smoothly over the sweep downward.
    – Alaska Man
    Sep 24, 2019 at 18:05
  • Got it, thank you. Would it be ok to use a slip joint where the santee meets the 90 degree elbows/AAV to allow for easier removal later?
    – peter
    Sep 24, 2019 at 18:10
  • I have never seen it done that way, I would not. I would use the threaded and teflon tape for a air/water tight seal. But it may be ok. ( not sure if it would be too code ) All your connections at the san tee and 90's should be glued with ABS glue.
    – Alaska Man
    Sep 24, 2019 at 18:17

Here's how I decided to plumb the traps. A straight 1ft section of 1 1/2" PVC was enough to get the AAV above the height of the strainer baskets. And I have enough room to get in there in the future. Had to get creative with making a double male union to join both female slip joints together where the santee meets the existing drain pipe, but it should hold up fine.

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