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Sewer smell only when water draining

Hi all,

First, given the number of sewer smell questions, I want to point out that I have searched a ton to try and find an answer to this question and I didn't come up with anything.

I have an issue on my top 3rd floor bathroom where I get a sewer smell in the shower but ONLY when the shower is draining and then only after 5-10 minutes. I.e. the smell comes only when the shower is in use and then only after a period of time. I don't get a smell from the sink or the toilet in the same room. The problem is intermittent.

I cleaned the drainage pipe to no avail and I checked the drainage of the trap when being used and it looks to be draining fine (i.e. water is filled the entire time and thus there looks to be a seal with the trap from gases below).

Problem occurs when the fan is on and when it is off. Only happens in this bathroom. I have noticed that the toilet leaks a bit at the seal (though no smell from there) and I am operating on the theory that the two problems are separate but thought I should throw that in.

Re: Sewer smell only when water draining

sound like p - trap is not holding enough water. p-trap probably too close to drain of the shower.

Re: Sewer smell only when water draining

a couple of thoughts, one being that the drain is not vented properly or the vent is too far from the drain. this would cause the water to gurgle, you might not hear or notice it, and when that happens it allows the sewer gases to escape. the second thought is that the shower might have a 1 1/2" drain pipe and showers are supposed to have a 2" drain pipe. this would cause the same thing i just mentioned above to happen. the height of the trap in relation to the height of the drain should not be a factor.

Re: Sewer smell only when water draining

I agree with MLBSF, for most of what they said. I know in North Carolina code allows for an 1 1/2" shower drain line. The p-trap can be no further the 2'6" away from the drain. Also, the toilet in that same bathroom need to be downstream of the shower and sink. On the upstream side will be the vent for all three fixtures.

The toilet has a p-trap built into the side of the bowl itself. Sometimes you can actually see the outline of it looking from the side view.

But the vent of the sewage gas is the issue. Have you gone above the ceiling to see the vent pipe coming from the bathroom? I know working on a 3 story house roof is kinda high, but the pipe should be ging up and through the roof. If the pipe is not there, the gas seeps back into the bathroom for the smell.

Good luck. Process of Elimination.

Re: Sewer smell only when water draining

Are you sure its not the hot water sometimes hot water can smell like sewer gas if the anode in the tank is bad?

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