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 Occasional smell from shower drain
Author: lbeachmike (NY)

Hi there -

We are noticing very occasional smell from the shower drain. We've only noticed it at night, and days apart.

If this is backflow of sewer gases, should I still notice water in the visible part of the trap at that time? All other fixtures in the house are operating normally and do not have any evidence of odor.

I do notice the shower drain water looks murky, but I'm not sure if that is typical or not. Is it possible it is not sewer gas, and the drain needs to be augered, or would there be obvious evidence of a partial clog?

Whatever the cause, I'm perplexed why it is only happening occasionally.

Thanks.

Mike

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 Re: Occasional smell from shower drain
Author: packy (MA)

the water in the trap would not have to totally go away in order for a sewer smell to come back up. it would only have to lose enough to lose the trap seal. although it should be noticable if it does lower that much. you would still see some water but not much.

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 Re: Occasional smell from shower drain
Author: North Carolina Plumber (NC)

In some cases a vent pipe will freeze over and allow a toilet to pull enough water from a shower trap so that sewer gas escapes. Maybe the standpipe coming up out of the trap needs to be cleaned ?

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 Re: Occasional smell from shower drain
Author: lbeachmike (NY)

Hmm - but tub drain is not having the same problem, nor is sink drain and they should all be tied into same vent ... probably in addition to kitchen sink and dishwasher.

It's not been freezing temps where I am - we are near the ocean, so it's warmer here.

Is there any way for me to prove the theory that it's the vent? If I can look into the drain and see a lower water level in that trap when it smells, that should be easy to determine because the water level otherwise appears to be pretty high up.

Is there any point in augering the drain?

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 Re: Occasional smell from shower drain
Author: North Carolina Plumber (NC)

I wouldn't auger it, just clean inside the pipe that's exposed above the water in the trap. Sometimes some odors can originate from that area. If you can see the water level in the trap have someone flush the nearest toilet and see if the water level fluctuates .

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 Re: Occasional smell from shower drain
Author: lbeachmike (NY)

This might sound like a silly question, but how much fluctuation am I looking for? I tried this previously - flushed the toilet right beside the shower, looked in the shower drain and noticed slight movement of the water in there, but the water level of the trap did not really rise or fall - more like a very light side-to-side motion.

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 Re: Occasional smell from shower drain
Author: packy (MA)

there needs to be enough movement to spill some water out of the trap seal and down the drain.
what you see is not enough to do this..

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 Re: Occasional smell from shower drain
Author: lbeachmike (NY)

Okay, so basically if I'm not seeing the water level drop at any time to break the trap seal, then it is not sewer gas coming from the drain? Can the gases bubble through the trap water at all or does it just not happen like that?

I do notice that the water in the drain is very murky. I don't know if this is typical/expected. But the most confusing part is that the odor is not there all of the time. It is there only occasionally. If I clean the drain itself, just do so with a soft brush like maybe a toothbrush?

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 Re: Occasional smell from shower drain
Author: packy (MA)

does the smell occur during periods of high winds?

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 Re: Occasional smell from shower drain
Author: lbeachmike (NY)

I'm not sure. We did have a couple of days of high winds here, but I don't recall if that aligned with the timing of the odor. We live in a beach town, so it tends to frequently be windy. I will pay attention going forward. What issue would the high winds cause?

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 Re: Occasional smell from shower drain
Author: packy (MA)

wind blowing over the vent stack can cause oscillation.

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 Re: Occasional smell from shower drain
Author: lbeachmike (NY)

By oscillation, do you mean that the sewer gases would be blown back through the trap water seal into our air?

This smell has not been there for a few days now. Tonight was pretty windy, but nothing. Though I suppose the direction of the winds will matter as well. I don't think this is the issue, but I will pay attention to the weather conditions when it next occurs.

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 Re: Occasional smell from shower drain
Author: lbeachmike (NY)

It turns out that this odor is occasionally coming from the steam vent of the 100 year old radiator in the bathroom. Usually the smell coming from the vent smells fine. But occasionally, it has a sour sort of smell like old pipe, which smelled to me similar to drain pipe.

Any plausible explanation for this? Particularly why this odor would only be there once in a while? The other radiators never have this smell.

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