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Thread: Intermittent Sewer Odor - Wax Ring?

  1. #1
    DIY Junior Member j p d's Avatar
    Join Date
    Nov 2012

    Default Intermittent Sewer Odor - Wax Ring?


    I own a single family home that has been converted into a 2-unit rental property. The upstairs tenant has been complaining about a sewer gas odor that comes around for two or three days and then goes away. I would like to get some opinions about what might be going on before I start ripping stuff apart. I only have one day a week that I can get over there and I don't want to spend that day working on something that is not likely the cause of the problem. I tried having a plumber come out twice but magically the odor completely disappears before he gets there.

    Here is some background:

    - The previous upstairs tenant told me that the toilet was rocking. I removed the toilet and found that the flange was cracked on one side so I replaced the flange and wax ring before the current tenant moved in. I am assuming that the ring sealed properly, and she says the toilet does not rock at all.

    - Shortly after the current tenant moved in, she started complaining about the odor. When I went up there, I could smell a faint sewer odor coming from the base of the toilet and nowhere else. So I sealed the base of the toilet for the time being until I had time to look into it further. The smell went away for a while but then she started complaining that the smell was coming out from under the kitchen sink which shares a common wall with the bathroom. There is a hole in the wall under the sink which would expose it to the main stack.

    - Last week the drain in the basement floor backed up when the downstairs tenant rinsed a load of laundry, I snaked the cleanout to the sewer and now the laundry drains fine, this has happened twice in the past two years. I don't think this has anything to do with the upstairs odor problem though.

    - There is no odor anywhere else in the house (first floor and basement) and all drains (kitchen and bath) flow properly so I don't think it could be a ventilation issue.

    Does it seem like the wax ring on the toilet might be the issue here or is there any possibility that the odor could be coming from somewhere else, making it's way through the walls into her unit and coming out that way?

    Thanks in advance! After two years of this problem I would love to get it solved for good.

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
    Join Date
    Jan 2008
    Land of Cheese


    It could be the wax ring, it could be a trap siphoning, it could be a cracked vent pipe, etc., etc.

    One method of finding the leak is to temporarily seal the building drain and roof vent and then use a smoke machine to pump smoke into the system. The smoke will show where the leaks are.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    If the vents aren't configured properly, stuff will drain, but it might end up getting sucked dry, or running so fast (as in an S-trap), where it flushes itself dry enough to negate the proper operation of the trap. If there's a drain that is not used often enough, it could evaporate, but that often takes quite awhile.

    If the toilet flange is not ON the top of the floor, you might need two wax rings to seal things up properly.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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