I am remodeling our master bath. There was a tub, shower, toilet and a double sink vanity originally. I've torn it down to the joists because I have to replace the subfloor (it was particle board.) In the remodel I will have all the above except no tub. I am looking to relocate the toilet to the opposite wall from where it was. The main waste line runs under the north side of the room, toilet will be moved about 8 feet to the south wall. The mystery (to me) - there is no visible vent anywhere in the room or its walls. Looking at the drain line as it goes back up under the house I can see nothing either. There is one vent visible on the roof, at the far end of the house. Does this make sense? All the drains worked fine, it seems.

Are the walls opened up? If the walls are covered, it's possible that the bathroom group is wet vented by a vent at the sink.

Walls are opened up - no vent where sinks are.

Was there an Air Admittance Valve (AAV) under the sink? These are a one-way valve that lets air in so the traps don't siphon but doesn't let sewer gasses out. I used these in several places in our 1917 home where I couldn't run up to a vent. AAVs let plumbing work fine in the absence of a physical vent, even if you didn't have them before I would suggest you install them on the remodel if you aren't going to run a physical vent up to the roof. Check local codes, they are allowed by IPC/UPC but prohibited by some municipalities and anywhere in MA.

This pic is the kitchen sink, the AAV is just off to the left.




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It may be “wet vented” from an adjacent bathroom on the 2nd floor
How about some pics of the bathroom demoed
Is there another bathroom on the same floor?



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I did have a plumber stop in to consult, and he recommended this same solution. There was not one in there before, but I will put one in. Thanks!!

Thanks for the reply - I do believe that AAV in the vanity is my solution.

Only if, I repeat IF, you can not run 'hard vents' to atmosphere.

AAVs are a 'bandaid' solution for OLDER solid brick or stone homes where it is TRULY impractical to open the walls for modern plumbing.

AAVs are mechanical with 'moving parts' which will, repeat WILL, fail long before the actual piping fails.

When (not if) they fail sewer gas WILL be released into the habitable space.

An AAV (albeit code minimum comliant in many jurisdictions) is NEVER best practice.

You do want good or best practice for your BRAND NEW bath, do you not ?!

'nuf siad

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Be sure it's in a place where you can get to it and change it when it fails 10 or 15 years from now. The "moving part" is a simple rubber flapper that creates a one-way valve, like a check valve for air. AAVs simply unthread and can be replaced in a minute as long as the valve is accessible. Do not install an AAV inside a wall without an access panel.

To misquote a movie: "I love the smell of sewer gas in the morning. it smells like money."

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638