Shower drain stinks when in use

October 4, 2021 2:31 PM

Around 5 to 10 minutes of showering, a sewer gas smell starts to come out of the shower drain. There's no detectable smell before turning on the water and it goes away after a short while after turning off the water (but not instantly). What could be causing this and how do I fix it?

• This is a walk-in shower stall. This is the main shower used, usually multiple times a day.
• The drain doesn't smell at all before the shower is used, even sticking my nose right next to the drain. However when in use, the smell is definitely coming from the drain. The smell is concentrated by the drain at the center bottom of the shower and can't be smelled outside the stall (unless you open the door).
• The sewer-y smell usually starts after the water has been running for about 5 or 10 minutes and does go away after the shower has been off for a little while, maybe an hour?
• Flushing the toilet in that bathroom before or after the shower doesn't seem to make a difference.
• This is either iron or PVC plumbing, not exactly sure.
• The water smells and tastes fine, including the rest of the house. This is an area with soft water and no sulphur smell or taste.
• The shower/bath in the other bathroom doesn't have this issue, but it's rarely used. As far as I can tell none of the other sink drains in the house smell.

Any recommendations for tips or next steps?

posted by WhollyMatrimony to Home & Garden (8 answers total)

if you have a stinky drain dump some hydrogen peroxide down there. Not sure what causes it. Gas bubbles maybe.
posted by The_Vegetables at 2:34 PM on October 4, 2021

How often do you clean/unblock the shower drain? They'll often get clogged with hair, which then collects gunk from conditioner and other things, and that can really stink when it gets hot and wet.

Many shower drains have a grille that can be unscrewed to give you access to remove hair and other crud.
posted by pipeski at 2:41 PM on October 4, 2021 [5 favorites]

It could be a fat build up from soaps & conditioners. You can get enzyme sticks you poke down the drain that can help with this. Clean out any solids from the drain and pop one of those sticks down there.
posted by wwax at 3:01 PM on October 4, 2021

This happens when the vent pipe for that particular drain is blocked. When you run the shower, and water goes down the drain, that water is displacing air (containing sewer gases), which has to go somewhere. When things work right, the air with those gases goes up your vent pipe and out your roof. If that pipe is blocked, the gas will bubble up through the trap under your shower drain (which blocks the gases when no water is running, and by indications is working fine). Assuming the water is draining OK, it is not any kind of blockage in the drain itself, but in the vent pipe.
posted by beagle at 3:04 PM on October 4, 2021 [13 favorites]

And yeah, the toilet uses something like 5 gallons maximum per flush and probably less. That's barely anything to a drain stack, but 5-10 minutes of even low-flow showerhead is going to be north of 15 gallons and can start blocking off proper venting. (Assuming modern fixtures, your shower uses as much water per minute as your toilet uses in a flush, roughly?)

I mean, the first step I'd take would be to run a snake down the shower drain to make sure you don't have a blockage from somewhere that's easily accessible to the homeowner side, but after that it's time to bring in a plumber and see if they can run from a drain clean out or if they need to lug an auger up onto your roof to snake out the vent stack.

Chemicals are basically delaying tactics - if you need to use chemicals, the problem will keep coming back. Physically extracting the hairball usually solves the problem for a lot longer.

If you're _not_ lucky there's been a shift in your plumbing and your shower drain is now on the wrong side of a water trap and is an easier vent than your roof vent. A plumber will be able to figure that out, too.
posted by Kyol at 6:31 PM on October 4, 2021 [2 favorites]

I was going to suggest exactly what beagle did - check the vent pipe for blockage. There is possibly a partial blockage of the drain somewhere after the sink and shower drain pipes join together.
posted by Short End Of A Wishbone at 10:52 PM on October 4, 2021

I'd make a point of not ignoring this - if it is sewer gas you want to do something about it as they can be bad to breathe and make people dizzy. If the concentration is really high they can be dangerous. Sewer gasses are the main reason why people resisted having toilets in their houses for so long.

It is very likely just rotting greasy matter in your pipes creating the smell but you want to be sure.
posted by Jane the Brown at 7:46 AM on October 5, 2021

Sewer gasses are the main reason why people resisted having toilets in their houses for so long.

They are but those were solved by the u-bends in plumbing pipes to trap gas. If you house is older than maybe 1980, then your laundry and much of your other plumbing probably doesn't have vent pipes. Your bathrooms and sinks might.
posted by The_Vegetables at 8:40 AM on October 7, 2021