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Two year old house: we are getting an occasional sewer odor from the shower drain after using the shower.

It appears that the water is occasionally siphoning out of the trap after using the shower. This issue occurred under the following conditions: While showering and standing on the shower drain, water builds up on the pan. Upon removing my foot from the shower drain, a large amount of water flows down the drain. I suspect this is when the seal is lost. I have to pour some water slowly down the drain to re-establish the trap, and then the odor is no longer detected.

There is no visible trap that one can see when you look directly into the drain, like there is in my other stall shower. The water is directed out the side of the drain, so a short offset must have been installed upon the final install.

Any suggestions???

user50826
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  • Is the trap accessible? i.e. The shower is on the first floor above a basement where you can access the trap in the ceiling. If not then changing it will be much more work. – ArchonOSX Feb 29 '16 at 02:24

2 Answers2

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A very likely cause, and one that is not too difficult to fix, is a partial obstruction of that drain (or even another drain) downstream or a partial or full obstruction of a vent pipe.

Are there any slow drains in the house? If so, snake them out. Go on the roof and inspect your vent pipe(s) for any debris, animal nest, ice plugs, etc. Run a large snake cable down the shower drain itself too.

Jimmy Fix-it
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You'll really have to get a visual, maybe with an Endoscope Camera. It should be a P-trap, but it's acting like an S-trap, which were essentially banned exactly because of this self-siphoning situation.

If it's an S-trap or the offset is somehow affecting the P-trap, then the only fix is to replace everything under there in order to remove the illegality or abnormality. Put in a warranty claim & have the builder properly eradicate the problem & repair all access damage for free.

Iggy
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