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Basement Shower Drain Gas Smell

9K views 10 replies 6 participants last post by  HandsomeMike562 
#1 ·
We recently finished our basement and installed a bathroom. Everything seems to be in good working order, except there's a brief sewer gas smell that comes out of the drain when the shower is first turned on. It doesn't persist, and it doesn't smell when the shower isn't running --- only right when the shower is turned on and begins draining (and it's not the water). The shower trap is full of water, and the sink never emits a smell.

Any help would be appreciated.
 
#3 ·
sir, you might have gasses being pushed down from above. i work in a hotel and when someone on the second floor flushes their commode it seems to push gas down along with the water and when it can the gasses escape and are hung up lower. they stink bad. i have only recently ran into this problem while we had a pipe open on a lower floor. when the water was used above us a terrible smell would come from the open pipe. it wasn't just stinky poop, it was strong gassy smell. i believe it was pushed down with the water and then trapped wherever it could get to. buddy builder.
 
#4 ·
I don't believe it's soap scum as we've yet to use the shower to actually shower in. I just run the water occassionally to ensure the trap is full and water hasn't evaporated out (we've had the basement finished for 3 months now)

Not sure on thegas being pushed down from above either - how would that make it smell only when the water is first initially turned on, and none thereafter or prior? it's odd to me. It's almost like a brief "puff" of the gasseous smell, and that's it.
 
#5 ·
If the trap and vent is proper....smell dissapears right afterwards? water smells fine at sink but doesn't enclose the gas or contain it as well ? happens "every" time? What's the age of the water heater? And your positive it's not the remains of last nite's dinner? couldn't resist that one!
 
#6 ·
If the trap and vent is proper....smell dissapears right afterwards? water smells fine at sink but doesn't enclose the gas or contain it as well ? happens "every" time? What's the age of the water heater? And your positive it's not the remains of last nite's dinner? couldn't resist that one!
I've rant the water for 3-5 minutes or so about 4 different times, and it's smelled each time, and the smell appears to go away after a minute or so.

I have no problems with the sink -- no smells whatsoever. The house is only 2.5 years old, so water heater is same age.

And yes, I am sure it's not last night's dinner! :laughing:
 
#7 ·
Okay! Have you covered that drain real good and ran the water? Hot H20 first, Then the cold H20 next? Isolate all your options. Run the H20 in the same fashion into a bucket too! Does the nose know the difference between sewer gas (methane) and hydrogen sulfide gas (rotten eggs) and all them other fun smells like the various adhesives you used during the install? Rattle off the ones you used if you can!
 
#8 · (Edited)
Sounds to me like a problem in the length of one leg of the P-trap. Methane (sewer gas) has a certain pressure and fills the empty tube behind the P-trap. If the one leg of the P-trap is too short, there's not enough water in the P-trap to prevent a burp of gas when you put water down the drain. So you smell it at the beginning only.

I think the key is to lengthen the P-trap low enough so the burb turns into a fart...sorry only way I could think of describing it. LOL

I have the same problem in the upstairs bathroom sink; I have to lower the P-trap an inch or so to ward off the smell. Bleach won't help unless there bacteria decomposing organic material down there.

This may be easy for me to solve than your situation. If the P-trap is in the floor, tough...!
 
#10 ·
Yeah, that's what I figured...if the drain is a 2" like most new drains nowadays, the problem may be less but if it's a 1.5" drain, maybe not.

Still not sure of my burp/fart theory tho', so I may be corrected by a pro sometime soon. But in my case, I changed the P-trap myself, didn't have the problem before I did that, and have the same symptoms now. When I get around to changing the distance on the P-trap, I'll advise.
 
#11 ·
Concentrate on the water. Turn on water and allow water to be caught in a clear glass of water. If you still have the smell you have ruled out drain,waste, and vent issued. Water if left in a remote end run will break down because off the oxygen content, there is a big word for it but I don't know it anymore. It is a powerful smell that is very simaliar to the smell you discribe. The water will also appear slightly brown, only slightly. How long it takes to break down I am sure depends on the water in your area. I am not an expert in this area, but you should NEVER have ANY sewer smell come back out of a wet trap.
 
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