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Thread: Trying to find source of sewer gas smell

  1. #1
    In the Trades mtcummins's Avatar
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    Default Trying to find source of sewer gas smell

    I manage a bunch of rental properties, and one of the properties is complaining of sewer gas smell. I smell it too upon inspection. It is in a sort of hallway section of a master bath. Along one side of the hallway is the walk in shower, the other side is wall with a doorway to a walk in closet. Right in this hallway is where I smell it most. Occupant complains of it in the closet most, which is open to that hallway.

    At first, I found 2 AAVs that were not sealing properly, was skeptical that this was the source, but asked for feedback from that fix. The smell returned.

    Owner tells me that this doorway from closet to hallway area wasn't there, he cut it in when remodeling. There were a couple of vent pipes going through there, which were routed around the new door. This was decades ago, but it does indicate that there are vents right in the area where we smell gas.

    I've checked all the traps (the never use the jacuzzi tub, so thought maybe the trap had just dried out), AAVs where applicable, and all toilets (2 near this area) are firmly mounted to floor with no wobble whatsoever to indicate a broken wax seal. There is laundry nearby as well, with a standpipe drain that I can't see the trap for, but I got no signs of sewer smell from the standpipe.

    A new wrinkle today, after a rainstorm last night, the basement was flooded. Around here, our sewer and storm water are in a combined system (yeah, dumb), so if we get enough rain, sometimes you'll get sewage backing up into basements. I don't know if the two are in any way related, but thought I'd mention it. We're going to have the main line snaked to be sure all is clear in the line, but could a backed up line be causing sewer gas smell in one location 2 floors up? Doesn't really seem like it.

    Thanks for your help
    -mike-

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    When they added the door, they may not have maintained a continuous downward slope on the vent lines when they jogged them around the doorway. They could be either plugged with debris or water or even just capped. Without proper vents, the traps could end up siphoned. An AAV can't be the only vent...there must be a functioning atmospheric vent in the system...and yours could be plugged. When you can smell the gasses, check the traps. Run some water above if you can, if you can easily hear the water running when you get close to the drains, the trap is likely dry. Run some water slowly and see what happens.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    In the Trades Jerome2877's Avatar
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    Find a plumber with a smoke machine, he can force smoke into the system from the lowest point and you will see the smoke if there is a leak.]

  4. #4
    DIY Senior Member kreemoweet's Avatar
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    A couple more guesses: 1) whoever reworked the vent pipes "forgot" to glue one or more joints, which have now come apart;
    2) remodelers used stinky Chinese drywall, which has gotten wet for some reason.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Odor sources are extremely difficult to pinpoint because the odors can move around the building, but you will only notice them when they accumulate in an area with minimal air flow. Years ago I and my helper spent hours trying to locate the source of a sewer gas odor. WE used smoke and peppermint, but could not even create the odor. Since it was getting late, I turned on the light in the bathroom and went to get some more peppermint. When I came back the homeowner said he smelled the odor. When I went into the bathroom, I smelled the odor and told him, "That is burnt plastic". I removed the shade from the wall light over the medicine cabinet and showed him the charred plastic when he had put an 'oversized" bulb in the fixture. New light fixture cured his problem.
    Licensed residential and commercial plumber

  6. #6
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    Peppermint test. That brings back some old memories. Not sure how you did it but we would put peppermint extract into a bucket of hot water and pour it into the system. The person that poured it in had to stay out of the building because he smelled of peppermint for the rest of the day.

    John

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