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 Sewer smell in bathroom sink
Author: steve8091 (WI)

Ever since I've moved into my house (about 6 years ago), there has been a terrible sewer smell coming from the master bathroom sink, particularly when running the water. Initially I would disassemble the drain and trap and clean it thoroughly, which would solve the issue for a couple of days, but it would quickly return. Based on the smell, and the fact that it is strongest when water is running, I strongly suspect that the vent line is somehow plugged. I have an unfinished basement, in which I can see a 3" line running into the wall behind the sink. Underneath the sink, there is a 1.5" line leading to the drain. I suspect that behind the wall, there is a T to which the vent line is attached.

My first question - does it sound like I have the problem correctly identified? Second, if I do, how do I go about unplugging the vent if I cannot access the tee? Are plugs more common near the T, or at the end of the vent on the roof? Is this something that I or a professional plumber could solve without tearing the house apart?

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 Re: Sewer smell in bathroom sink
Author: Nayman's Drain Services (Non-US)

Have you cleaned out your overflow?
With water in the trap, there is no way sewergas can work it's way up to your nose.
Pour some bleach down your overflow, and if you can, brush it with a baby bottle brush as best you can.
Let us know what happens please?


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 Re: Sewer smell in bathroom sink
Author: jblanche (WI)

Is it a hydrogen sulfide aka rotten egg smell?

Is it possible the smell is coming from the water coming out of the tap?

Is this sink one of the highest fixtures in the house?

Do you have city water or a private well?

Do you have a water softener or water heater that needs disinfection?


Regarding the matter of cleaning the trap and it being solved for a couple of days, could it be that running a large quantity of water eliminates the buildup at the high point in the system?

Links to the State of Wisconsin Plumbing Code:
I am not a plumber.

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 Re: Sewer smell in bathroom sink
Author: steve8091 (WI)

Thank you for your replies thus far.

I'm reasonably confident that it is not the overflow, as I have cleaned that with bleach and/or vinegar in the past. I will certainly give it another shot and see how that works. My thought as to how sewer gas is escaping (and I could be wrong) is that because the vent is clogged, sewer gas is rushing to replace the space vacated by the draining water. If it was the overflow, I wouldn't expect it to be stronger when I run water down the drain..?

It is definitely a sewage (and not a rotten egg) smell.

We live in a 1-story, so most all of our plumbing is at approximately the same level. Certainly of the sink, tub, and toilet in that bathroom, it is the highest fixture.

We do not have a water softener, and our water heater was actually replaced recently when the old one went out (the smell was there before and after the replacement).

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 Re: Sewer smell in bathroom sink
Author: Wheelchair (IL)

When it comes to lavatory or overflow, I like the foam acid cleaners as they expand in the drain to cover the inside of the tubes and pipes. When all fails, consider the wax gasket.
A good sniffer often reduces the time to find the offending odor.

Best Wishes

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 Re: Sewer smell in bathroom sink
Author: tato

Check under the building maybe a broken pipe leaking under the house????

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 Re: Sewer smell in bathroom sink
Author: Prudoco (FL)

Did you figure out the problem with the sewer odor???

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 Re: Sewer smell in bathroom sink
Author: Ztrauq (CA)

I would wonder does the smell occur if you run a low flow of water through your sink. It could be the volume of water. Since this is in the master bath, does the smell also occur if you run water through the shower? I'm guessing that they are close enough that they share the same drain line and vent pipe.

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 Re: Sewer smell in bathroom sink
Author: Artman06 (PA)

Fill your sink with water, then let it drain, if it gurgles after the sink drains you have a vent issue, (install a auto vent under the sink) if thats not it then its most likely sulfer in your water. ps. never mix bleach and vinigar it creats a toxic gas!

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 Re: Sewer smell in bathroom sink
Author: mamafli (CO)

I don't usually respond to blogs but found this one particularly helpful and wanted to share my stinky sink story in case it helps someone else avoid going through the frustration I did. So, both of our master bath sinks are stinky when we run the hot water. At first we thought it was the hot water specifically so our plumber suspected it to be the anode rod inside the hot water heater. And, that the rod was going bad sooner than usual because we also have a recirculation pump to help expedite getting the hot water up to the master bath. This was NOT the case however and glad we didn't just automatically change the anode rod or get a new hot water heater. This was determined upon further detective work as I realized it was not the hot water that smelled because the problem is only in the upstairs sinks and not anywhere in the house. I took a cup, filled it with hot water from the master sink, sniffed it and it smelled fine. But if I go over to the sinks...stink!

Next we suspected the drain vent was clogged so we called a company that cameras the line. The tec was great that did the video and it was fine. Once we explained the symptoms further to him, he was absolutely certain it was not the drain vent or sewer gas because, if it was, the stink would be constant all the time, not just when the water is running. And the stink would be wafting all over the room and not just isolated to the sink bowl. Good thing because ripping out the drain vent would be a major deal. And he was really nice and only charged the trip charge since he felt the scheduler should have clarified our symptoms and realized it was not an appropriate service call in the first place.

Sooo with his suspicion that the stink was localized to the sink itself or perhaps the faucet I proceeded to "sniff" more specifically inside the bowl and discovered it was worse coming from the overflow hole than the drain. Hummm....Seemed like the stink was rising up from the overflow hole from the water running and pushing the stink upwards. Plus the overflow hole looked really black and icky.

I called my plumber and gave him a "sink stink update" and he said to pull up the drain plug to keep liquid from going down the drain. Then to pour 1-2 cups of bleach into the sink. (I didn't measure. Just eyeballed it and it seemed like a lot of bleach.)
Then he said to run the hot water into the bleach and let it mix together until it filled up and ran into the overflow. While it was running into the hole, I took a tooth brush and tried to scrub out the black gunk but I could only get it into the hole little bit. I let it pour down the overflow until the water looked more clear and the bleach was more diluted and unplugged the drain. As the water was running down the drain, I took a cup and scooped the diluted bleach/water up from the bowl and continued to pour it into the overflow. I did a good rinse that way, waited about 15-30 minutes and came back and rinsed the overflow with fresh hot water.

Result...stink is gone 1 day later. It seems to waft more of a bleach smell when I run the water but that is a HUGE improvement to the sulfur stink and I think that is getting better too. The sinks are 8 year old Kohlers so I don't know if this is typical maintenance but I have never lived anywhere before that needed this done to the sink. I will call Kohler and see what they say about the sink design etc but if this is all I have to do once in a while, I can live with that...hate putting bleach into the sewer though. One other thing is I will look for a skinny flexible brush to get further into the overflow drain to get better access to the black grime.

Hope this helps some of your stinky sink problems! Good luck.

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 Re: Sewer smell in bathroom sink
Author: Danka (CO)

I've read all your situations and solutions, (including the bleach). Here's my story and why I think we need more help and input.

I replaced a faucet 2 years ago on a sink about 20 years old. Before the new faucet NO SMELL. After the new faucet sewer SMELL coming up from the overflo.

Then February 2014 we have a bathroom remodel on our 1950's home. Everything's new! Toto sinks, nice faucets, new plumbing to accommodate 2 sinks instead of the 1 we had before. So, like i said - - - it's all new and we still have a smell from the overflow. It doesn't matter if it's hot or cold water. I don't get it. Before any remodeling there wasn't an odor. I wonder if I should get some bacteria type product to pour in, as used in septics. We're on city sewer but something doesn't make sense here.

Is there any professional out there that has experience in this???

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