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Just move into a new apartment which is on the upper floor of three. The bathrooms of each apartment are directly above one another. I believe that the exhaust vents of the bathrooms in the apartments below are connected to the main soil waste pipes, as is the exhaust vent in my own bathroom. I know they should be separately vented but these are old Victorian properties with no other vent options for the flats below. I can easily install separate venting for my own bathroom fan.

I have noticed a drain smell since moving in. I have just discovered that:

  1. The 4" waste pipe is connected to the 3" roof pipe with gaffer tape. The connection is under my bath and effectively unsealed with the result that the waste pipe vents into my bathroom.

  2. To make matters worse, there is another break in the 3" pipe behind the tiled rear wall of the bathroom. It is impossible to reconnect it to the roof vent without breaking into the wall.

So even if I fix the connection under the bath, the waste pipe will vent behind the wall.

My question is, can I just cap the waste pipe where it terminates under the bath with an air admittance valve, bearing in mind that the exhausts from the bathroom fans below vent into the waste pipe?

My concern is that the fans could cause a build up of air pressure in the waste pipe. Would the air just escape down the sewer?

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    Apartment, as in you rent - make a stink (pun freely intended) to the landlord, and get it fixed right (yes, breaking into walls as needed.) Apartment but you really mean a place you bought (ie, some would call it a condo) you need to sort out who is responsible for what, where - but the end result is that you still need to fix it right - it's just going to cost you more, probably.
    – Ecnerwal
    Commented Dec 18, 2013 at 0:43
  • Yep, I bought the place. I'm from the uk - apartment here doesn't mean rented. Just another word for a flatted property.
    – David Kerr
    Commented Dec 18, 2013 at 0:58
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    I can't imagine an air admittance valve would be acceptable to vent all the drains in a three apartment building from a practical standpoint. Your fix doesn't pass my smell test. You might have to do a proper fix. Does your building have a fund for this sort of thing... Do you pay maintenance fees?
    – Edwin
    Commented Dec 18, 2013 at 1:50
  • As mentioned, you cannot use an AAV because of the fans. A proper fix would also involve properly venting fans separate from the waste vent. Even then, an AAV is not a solution, as they are for individual fixtures, not a waste stack vent for multiple bathrooms. I do recognize the issues with venting fans and admit using the waste vent is a clever albeit illegal solution. Fixing the vent through the roof will get everything working even if it's technically still wrong.
    – bcworkz
    Commented Dec 22, 2013 at 20:30

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See comment above, this is a condo/owned property, not a rented apartment.

Since the other bathrooms vent into this pipe you cannot simply cap with an AAV. The air flow from the fans will dry out and empty traps, leading to sewer gases elsewhere.

You need to break into that wall and fix it properly.

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