I'm adding a kitchenette to my basement and am looking to tie into the existing drain line for the upstairs sink to add the new sink. The sink upstairs is not roof-vented, but has an AAV. My thought is to cut the metal pipe above the clean-out fitting, extend the plastic pipe down, and use a fitting to connect the new sink drain. Off the new sink drain, I'd add a fitting and run a pipe for the AAV. I'm thinking about running this up through the wall cavity, through the floor, and into the upstairs sink closet so that it remains accessible without needing an access panel on the downstairs wall.

A few questions: Is this overall approach ok or is there a better way? I'm a little confused by when to use a wye vs a sanitary tee vs a regular tee, can you help me with what is appropriate for connecting the trap line of the sink to the existing drain pipe and for what fitting to use on the trap line to connect the AAV? Thanks!


  • All these questions relate to your project, but you've really got 3 different questions all rolled into one, and that doesn't work really well here. Please edit this down to just one question, then feel free to ask the other 2 questions as stand alones. You can link to each other so people can see the full scope if you'd like.
    – FreeMan
    Commented Oct 19, 2023 at 20:20
  • In a project like this there are obviously multiple questions. With that said, your post is just fine, no need to change. The new sink could have its dedicated AAV
    – Traveler
    Commented Oct 19, 2023 at 20:33

1 Answer 1


You're overall approach is fine so long as your local authority having jurisdiction allows the use of AAVs. The only better way is to have an actual vent pipe.

Regarding the use of wyes, sanitary tees, and regular tees:

Typically, when following the flow of the drain, you can use a 90° elbow (or sanitary tee) when changing from horizontal to vertical, then when changing from vertical to horizontal, two 45° elbows (or a wye and a 45° elbow, or in some locations a combination wye). Use a wye when branching off a drain on the same horizontal plane. Regular tees can only be used on the venting portion or as a two-way cleanout.

There are some exceptions, such as a toilet is connected with a 90° elbow even though the drainage is vertical to horizontal. The same applies when connecting a double bowl sink.

Here's a sketch of your situation and what fittings I would use: enter image description here

  • Thanks so much! This is exactly what I was looking for. Commented Oct 19, 2023 at 22:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.