I bought a new house about a month ago, and have since noticed some plumbing issues in the laundry room:
- laundry tub drains slowly
- occasional "musty" smell, which seems to come from the drains
I did some research online and found that lack of drain ventilation could cause both of these problems. So I checked the plumbing and it looks like both the washing machine and adjacent wash basin drain into the same pipe. As far as I can tell, there is no ventilation on these drains (photo below); it looks like a stacked pair of S-traps.
The laundry room is in a little addition at the back of the house. So I probably cannot tie this back in to the main house venting stack without a lot of work. I gather the simplest solution is to locally install an air admittance valve (AAV). Does that sound like a reasonable approach here?
If so, am I on the right track with one of these:
My plan is to remove the upper S-trap. Then install a sanitary T, going to: AAV (top) and P-trap (horizontal). Does that sound right?