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 Sewer gas from shower drain
Author: jramig3 (MO)

I live in a 4 year old house with a separate shower in the Master bath. For the past few weeks there has been a sewer smell in the bathroom and last night I traced the source to the shower drain. There is a P-trap installed and the water level seems sufficient in the trap. Another neighbor with the same floor plan indicated a similar smell and contacted a plumber. She was told the trap wasn't installed correctly and that was the problem. I didn't fully understand what was incorrect about the installation from her description but it seemed to be something related to the street L from the trap to sewer pipe. I'm looking for guidance from anyone who has dealt with a similar situation.

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 Re: Sewer gas from shower drain
Author: packy (MA)

if you have a p-trap below the shower and you can see water in it and you still smell sewer gas, the smell can not be coming from that trap.
i can not think of a reason the "street ell" would cause any problem if there is still water in the trap. i have installed thousands of traps and they all have "street ells".

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 Re: Sewer gas from shower drain
Author: hj (AZ)

Unless you are not telling us the entire story, that plumber was trying to make a major repair because he did not know the real cause, and probably didn't care as long as he got his check.

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 Re: Sewer gas from shower drain
Author: jramig3 (MO)

I know for a fact the smell is coming from the shower drain since it was MY NOSE doing the smelling of that drain. Does anyone have any real suggestions for the cause?

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 Re: Sewer gas from shower drain
Author: strap

It could be vented incorrectly. I have seen shower traps that when a stool is flushed, or a full whirlpool tub is drained the water moves enough in the trap to allow gas by.

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 Sewer gas from shower drain
Author: Wheelchair (IL)

Guidance- is so uncommitted and may offer answers without the benefit of actually witnessing the problem, as we are merely hearing the effects.

Eliminate the speculation and hire a licensed plumber in your area that is trained in those areas to find the real culprit.

Yes, it could be the trap or lack of a real trap or it could be a vent problem.

It could be defective piping or drains. It could be a restriction or a blockage.

It could be most anything.

Spend some pennies to save some dollars and have peace of mind knowing that you have a clean system which is properly vented.

or you could continue to speculate....

Best Wishes

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 Re: Sewer gas from shower drain
Author: hj (AZ)

In that case the odor has to be either from material coating the pipe, or stagnant water inside the floor that is pushed out when you walk on the shower floor. If you have water in the "P" trap, and the trap is installed even slightly correctly, (and you do not see a side opening into the drain riser between the trap water and the shower floor), there is ABSOLUTELY no way sewer gas can enter the room through that drain.

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 Re: Sewer gas from shower drain
Author: hj (AZ)

But in those cases while water is still lost from the trap, but enough is retained so that when the negative pressure ceases, the water falling back into the trap will be adequate to restore the seal. Sewer gases cannot flow into the room during the negative pressure phase, and afterwards the trap will still be effective.

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 Re: Sewer gas from shower drain
Author: jb44

had the same problem a couple of years ago. popped the drain cover off and sucked out the water from trap with shop vac, filled trap with bleach and let it stand over nite, brushed trap and piping above water level as good as i could with a long handle brush. rinsed out and have not had any problem since. hope this helps.

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 Re: Sewer gas from shower drain
Author: redwood (CT)

Smells coming from a shower drain can have causes ranging widely. Some of the causes I have seen are:
*Water reacting with the anode rod in a water heater causing the smell in the shower area.
*A smelly buildup of crud above the water line of the trap.
*A leaking vent for the shower.
*A partial clog or back pitched drain line allowing drain water from other (smelly) sources to mix with the water in the trap.
*A leaking trap or improper venting causing loss of water in the trap.
*Gases coming from a roof vent through a roof opening too close to it.

The cause is not always easy to find even for a pro. One word I will give is don't rule out that the smell is caused by something higher than the drain. Many of the "sewer gases" are heavier than air and can settle onto the floor of the shower.

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 Re: Sewer gas from shower drain
Author: strap

Hj, where I have seen the water pulled in the trap. Enough of the water was pulled down the drain that the trap lost its seal, so sewer gas smell until the water was ran in the trap to fill it back up.

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 Re: Sewer gas from shower drain
Author: hj (AZ)

Not to argue, but it must have been a low seal trap. Most proper ones would retain enough water, at the point where they started sucking air, to drop back and restore a marginal seal to the trap. Unless it continued long enough, and the air was moving fast enough, that even that water was aspirated by the air moving past it. The old "bag" S traps were designed specifically to retain enough water to reseal the trap after siphonage occurred.



Edited 2 times.

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 Re: Sewer gas from shower drain
Author: kalia (CA)

Hi, Did any of you solve this problem? I have a TERRIBLE sewer gas smell and I have tried everything in this column and then some! I've replaced the p-trap, added a second one, snaked and camered all the lines and all the vents, installed new vents, had smoke tests done, had 4 plumbers look at the problem, cleaned the drains and all the pipes with cleaners and brushes, used bleach, draino, pipe cleaner, pro biotics, replaced my main lateral line, filled the vents with water to detect blockages, opened up all the walls to look for leaks or broken vents -- NOTHING has found the problem! Please help!
The smell comes ONLY after or while running the shower. If I cover the drain and run the water, there is no smell. It's MUCH worse if I uncover the drain and let a large amount of water drain at once. It goes away a little bit if I don't use the shower for a month, but then comes back full force after using it once. Any ideas?

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