Complex Sewer Gas Issue

Rustyshack

I have sewer gas coming back up my master shower drain. I only smell it after taking a shower. There is water in the trap. I can see tiny bubbles appear in the trap water after running the shower for a short period of time and turning it off. Also there is movement of the trap water...like the water is bouncing up and down in the trap after running the shower. I have had 4 plumbers look at this. Smoke test revealed "smoke" odor from around the toilets in the OTHER bathrooms. None in the master bath. Smoke came out of the shower vent. Another plumber ran a camera from the clean out up the vent. He said the vent was clear and unobstructed. It is definitely sewer gas-not mold or bacteria. How can sewer gas come back up through the trap water if the vent is reported clear???? Thanks for any help.

AllanJ

Could you have a leak in a drain pipe under the floor and after the trap? It could be in a location that does not get the downstairs ceiling all wet but does let sewer gas escape.

If you put some bleach (two ounces should be enough) down the affected drain and let it sit overnight, would the smell go away in a day or two? (A "drum trap", common for bathtubs in homes built before about 1960, may need 4 ounces.)

Decaying matter may have collected in the trap for that drain, generating the sewer gas right there.

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Rustyshack

I have a one story house with the pipes in a slab foundation. We always pour a little bleach down the shower drain after a shower which stops the odor. There is a separate tub that sits beside the shower and is "down line" i.e. in the direction the drain pipe from the shower to the sewer runs. Never smell any odor from the tub drain. Not sure if the tub, which looks like it could tie into the same drain pipe as the shower, could have anything to do with it ??? Thanks