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!