I have random sewer odors coming from my tub and shower drains. They are separate in my bathroom. I have had plumbers come and clean the drain, but that is not fixing the problem.

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    Did the plumbers check the venting? – Comintern Apr 6 '15 at 1:21

You have sewer gas. Water in your plumbing traps is supposed to prevent that. There's some problem that is resulting in not having a water seal in your traps for these items (they may share one trap if it happens to both at the same time.)

If you pour water down the affected fixture (slowly) does the odor stop shortly thereafter? Or, if you carefully do this after each use, does the problem not occur (since it can be hard to tell when an odor stops coming in, if it's lingering around the bathroom.)

If so, you may have a venting problem, with the traps being sucked dry when lots of water goes down and creates a siphon (what venting is supposed to prevent.)

How old is the house and/or the bathroom? Another common possibility for an older house is that an old drum trap has failed, and is not functioning as a trap at all anymore. "Pouring water slowly down the drain" would have no effect in this case.

It's surprising that plumbers would not have mentioned or investigated these possible causes, unless they were only asked to clean the drains, rather than to identify and solve the smell problem.

  • I live in a townhouse which is 27 years old. The plumber was called because of the smell which comes and goes. He couldn't smell it when he was here so he focused on cleaning the drain. He did not mention traps. I never use the tub, which I think shares a drain with the tub. It was suggested to me that it might be drying out due to lack of use so I pour a cup of water down the drain occasionally. But I still get the smell. Can I check the venting or do I need a plumber? – helen Apr 8 '15 at 15:44

Is that bathroom used much? Our 3rd bathroom tub never gets used. As a result (we surmise), the water in the drain evaporates, allowing sewer gas to find its way into the house. We just run the tub for a minute every week or two to fill the drain. Haven't had the problem since.

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    In regards to adding water periodically in unused drains, I've heard that after you do that, add a small amount of olive or cooking oil. It creates a thin layer above the water that slows the evaporation process. – Brett McCann Apr 9 '15 at 21:09
  • Reminds me, I need to pour a bucket of water down the shower drain at work. I do it about every 4 months because the water evaporates out of the trap and sewer gas starts backing up into the bathroom which then leaks out into the lunchroom. Good idea on the cooking oil. – Fiasco Labs May 26 '15 at 14:47

I had the same problem after I had my bathroom remodeled. I just pour some vinegar down the drain and it goes away. I'm not sure what caused it but the vinegar solves the problem for now. I had to do it a few months ago.

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