Laundry Drain Trap

[Cookiemonster]

Just a DIY'er here. I'm in the process of trying to clean up some plumbing work in my laundry room, in order to place the water lines and drain/trap inside the wall (first pic is a "before"). Initially I thought I needed to add an AAV since there is no vent. However, in the basement, it looks like there is a horizontal wet vent set up (I think thats what it's called). My question is- since the whole drain system is technically vented, can I just add a 90 to my setup in the second picture? Or would it be recommended to keep the T and add the AAV instead? Just pretend like the pipe after the trap is full length, lol. Thanks in advance.

 

[wwhitney]

You must provide a vent at the elevation of the trap (before the trap arm falls more than one trap diameter). So yes, you need the san-tee and an AAV in an accessible ventilated box at least 4" above the trap arm. The "before" picture was an illegal S-trap.

Cheers, Wayne