The sink's vent pipe (it normally connects to the main vent pipe later) could be blocked. Do you hear a "glug, glug, glug" when turning on the water? Then it is the vent. Are other fictures draining more slowly than usual? That is evidence number two.

Installing an air admittance valve on the sink will probably solve the problem.

Cheers, Luxurino

Thank you, thank you, thank you! I’ve not noticed any other fixtures draining slowly, and I’m not hearing any “glugging”. I’ll definitely be looking into the air admittance valve.

The odor may be coming from the overflow hole. Often times a build up of toothpaste, soap residue, etc. linger in the area between sink base and pop up drain assembly. Remove the pop up drain, brush the area clean, then spray or pour some kitchen & bath cleaner down the overflow. Let it soak, rinse thoroughly with hot water.

Thank you, Brushworks. I have taken out the pop up drains and cleaned them. Everything looks clean as a whistle.

I will be following closely as I have a similar problem in the 50's house I bought a few years ago. There was no noticeable smell before the only bath was gutted after house reno. Same as you've noted, no smell from the tub, kitchen sink, or my utility sink in basement. For the first 6 months to a year I used an organic liquid soap until daughter called one day and noticed a mold/mildewy ? sewer smell at her house which she attributed to using the same soap. I began noticing the same problem - she changed soap, used boiling water, and her problem went away; mine has not. I really cannot use bleach as I'm on an ancient septic system. The smell is so bad I stopped using the sink last fall; the smell is still awful when guests use it. I also cleaned the drain which wasn't very dirty. I live by myself. I hope someone has a solution for you!!!

I might be able to help both of you and only ask that you post results of this test. Draw water in a pitcher from kitchen faucet. Pour water in bath sink at approximate stream which normally come's out of bath faucet. Do you notice the usual odor or is it absent while pouring from pitcher? If odor is absent, I have the solution.

Pex supply pipe may cause odors

@klem1: I can’t believe it! I just performed your “pitcher test” and there was absolutely no oder when I poured the water down the drain. I turned on the tap immediately after I did that and got a nose full of sewer smell. Dying to know what this means and how to fix it! What is the connection between the faucet and sewer smell? Do tell!

I’m back.... just did another little test... practically stuck my nose in the faucet as I turned on the water into a glass. The smell is definitely coming from out of the faucet, but it’s not the water itself. And here I’ve been blaming the drain pipes!

Clean the aerator. Or rub your finger over it. What did you find?

I can’t get the aerators out, unfortunately. They are kind of recessed in the faucet. I’ve scrubbed them with a toothbrush and bleach, but it didn’t seem to make a difference. They were brand new faucets though and the smell has been occurring from the first day they were installed. The mystery continues....

The end of the faucet should unscrew, so you can get at the aerators out to clean them.

I didn't see one in your pictures, but you might have a blocked auto vent (or studor vent) if they did not vent your sink directly outdoors. If you have this type of vent it will start to smell like sewage when the vent is blocked every few years. (Just a $15 quick part to replace)

Thank you, everyone! I will take all this info to my plumber and we will troubleshoot. I hope this issue can be resolved. Even if it is harmless I would like it gone. I'll be sure to post to advise if the problem has been resolved or if it continues. Thanks again! You've all been helpful!

Before you spend a bunch of money on a plumber try putting some bleach or squirt some toilet bowl cleaner down the overflow hole in the front of the sink. I’ve had this problem before and that always takes care of the problem. Certainly worth a try!

Klem, I think you've got it. I've noticed an H2S odor from hot water in various cases a few times over the years, but I never would have thought of that in this case. Your explanation makes sense. Nicely done.

Thanks, Mimi. I’ve given that try and to no avail. My mother is constantly battling that sulfur smell from her hot water tank, so I’m familiar with that problem to some extent. I’m not sure that is what my problem is, as the oder I get is distinctly sewer. It’s either that or a vent issue. I’m willing to give all suggestions a try! My plumber neighbour has to come this week to do other work anyway, so he’ll just tack this onto his bill. Fortunately, he’s reasonably priced!

Well, it’s back to square one. The plumber was here and our hot water tank does not have a rod in it. My husband told me it doesn’t take one, but neither the plumber or I really believed him! Our water is heated by an oil furnace and a few years ago we had the oil company install a holding tank. We were finding it took so long to get hot water coming to the tap, so the tank keeps the water hot and ready when it’s needed. But about the smell... to recap: it’s distinctly sewer, not sulfur, not a hard water smell. And it’s only coming from the faucets in the upstairs bathroom double vanity sinks-not the shower, not any other sink in the house. The bathroom sinks are under a year old (although the smell was still present with the old sink-just less severe and less frequent). The sinks are sparking clean. I’ve removed all the little parts and cleaned them. The plumber checked the drains and they are all clear. And it’s not the water itself that is smelling. We are on a well, but the water is crystal clear. It’s definitely coming from those two faucets, and just when you first turn on the tap after it’s not been in use. I’m afraid I’m going to have to learn to love this sewer smell. I don’t want to, but maybe the only solution is a $4000 water treatment system. If anyone has any other (more economical) thoughts I’d love to hear them!

Hmm, I wonder if your new faucets are reacting with something in your well water and causing a bit of something odorous to build up until you turn the tap on.

Anyway, I got a bathroom faucet last year and it came with a little plastic wrench doohickey to remove the aerator with. Looks like a cylinder with a jagged end to fit the special fitting on the faucet, with a handle on the other end so you can turn it. Did you get anything like that with your new faucets?

Did you say you checked your drain vent lines and they are clear, all the way to the roof? One way is to go up there and pour some water down the vent pipe and make sure it drains.

Klem - After my post I squirted hydrogen peroxide into the sink's overflow holes, and haven't used it since until now when I tried the pitcher of water you suggested. The results were sort of inconclusive, (so I will repeat it later tomorrow) as initially I did not notice the smell as I normally would, but then a kind of a 'big whiff of smell came out. I squirted in a little more HP, but not a lot as I need to buy more.

My kitchen sink is close above the hot water tank; the water comes out very hot fairly quickly. The bathroom sink is further and the bath sink and tub water takes a long time to get hot so I'm sure they are both plumbed post kitchen connection.

No sulfer smell, and the tank is not conventional - it is from the mid 80's- an indirect tank. The smell is a moldy-mildewy-sewery smell. That smell does not come out of the adjacent tub faucet or drain, nor even a hint from the kitchen sink. or the SQ stack unit which I forgot about before, located in the kitchen - oh and not the Bosch dishwater, either. The water itself has no oder. Sigh.....

Are the drain lines vented for that particular sink? If so, it would be to the outside, and probably through your attic and out your roof, unless it has been joined into another vent line. Could it be clogged? A few years ago, I had birds build a nest over one of mine. They didnt occupy the nest very long. :-)

So that’s what that doohickey is for! I’ll give that a check tomorrow. Yes, the sinks are vented to the outside. In a couple of the pics you’ll see that black vertical pipe. I think that’s the one that goes through the attic and roof. I have not checked it from the roof. The plumber doesn’t seem to think it would be clogged (but I’m not really sure how he knows that). I always assumed that was where the smell was coming from, but since doing the test with the pitcher of water I’ve discovered the smell is coming out of the faucet and not the sink drain. So, unless sewer gas can get from the vent pipe into the faucet, I’m baffled. I really do appreciate everyone’s help. My furnace is due for a cleaning next month so I’ll ask the technician about the hot water tank to see if a rod could be installed somehow. Maybe that would solve it. I don’t know. Thanks again everyone! I appreciate your kindness!

I've been reading up on this topic and I think your problem might be with the stack vent (drain vent) that allows sewer gas to exit your plumbing. You might have a blockage to that vent and that's why the sewer gas isn't venting properly and coming up through your sink. Here's a link to a YouTube video where the TV show, "This Old House" cleans out a blocked stack vent (drain vent) which will show you what the problem could be at your house.

Here's some more information about this problem from Mr. Rooter Plumbing website that provides a good explanation.

"Plumbing vents are required in most drains around the home, such as toilets, tubs, sinks, showers, and floor drains. In most plumbing systems, the vents lead to a single vent stack located on your roof. Vents serve two main purposes: first, they allow sewer gases to escape the system safely, and second, they introduce air to regulate the pressure inside your plumbing so the system can drain properly. Without proper venting in place, sewer gases could become trapped in your pipes and seep into your home, making you uncomfortable or even ill. The right balance of pressure inside your pipes is necessary to allow gravity to draw wastewater away from your fixtures, rather than letting it back up due to the vacuum left behind when water moves through the pipes."

PDJH: "The smell is definitely coming from out of the faucet,"

If the odor is coming from the faucet, then it's not coming from the drain, yes?

So why are some comments here still telling you to look at the drain for your problem?

And why are you still looking at the drain for your problem?

Have we all slipped into some universe composed of "alternative facts"?

Is going down the drain line here the same as going down the rabbit hole?

Same problem. Well, I only smelled the "sewer smell" for a brief period, but the sink gurgles and sounds like water drip in walls for a few seconds after running (hot) water.

Sound's like you actually do have a drain problem Waynette so you should try what everyone is saying. I'm looking foward to hearing all the reasons why hot gurgle's and drips but cold doesn't.

My apologies to pdjh, the OP, for barging in on your thread. I do want to ask why if my bath sink's smell comes from the drain and may be vent related, why isn't there a smell emanating from the tub? My house is from the 50's, and there are only 2 vent stacks; one above the kitchen and the other near the bath.

Welcome to the rabbit hole Rose,come on in and make yourself at home. While waiting for the next adventure,I will ask you a question. What would you tell your neighbor in the following scenario?

The neighbor say's Rose come to my office and tell me where you think an unusual odor is coming from and what it smell's like to you. (At which point,neighbor spray's the room with scented air freshner and ask's "what do you think?")

I’m ok with others jumping in on this thread with their similar issues. I feel mine is about as solved as it’s going to get right now. Reason why I still listen to people’s comments/suggestions about my drain/vent, even though I now know the smell is coming from the faucets (although I didn’t realize this when I started this thread) is because I know nothing about plumbing, so for all I know there may be a connection between vent and faucets. If that’s impossible I’d like to know! So at this point I’ll talk to the furnace technician and see if a rod can be added to the hot water tank. Common sense tells me that’s my best bet. Hope all the others who have jumped on board here can get their issues solved!

Thank you pdjh! And Klem, thanks for your welcome, but I don't understand your second paragraph. Smells a little like sarcasm, but even if it's humor, it's flying over my head. Sorry.

Can anyone answer my question regarding the 2 vent stacks on my roof; since there is only one apparent vent stack for the bathroom, wouldn't the smell if it is coming from the sink drain also be apparent from the tub since they seem to share the same vent? Also, is hydrogen peroxide harmful to septic like bleach can be? I explained way upthread my septic is 60 years old. I try to be super, super cautious about what I send down the drain. I want to pour a lot more HP down the over flow drain holes but I'm afraid...

Klem, I will repeat the pitcher of water again tonight. Thanks everyone. I am tired of having to brush my teeth etc. in the kitchen to avoid the nasty bath sink smell. : (

Rose you are studying stinky sinks and I'm studying human nature. I've tried helping you,do you not feel the need to reciprocate? Call it what you may but there's times when keeping it light help's one not to cuss then lay down and cry.

LOL klem, I must already be down the rabbit hole because I don't understand at all what you are saying - and seriously that is what makes me really want to cry! Reciprocate? What? You are confusing me.

Rose, my guess is that your bathtub drain isn't emitting sewer gas because it has a more effective trap than the sink does. A tub will often have a big drum trap. And especially in an older house, the sink may well have an S trap (goes down through the floor) rather than a more modern P trap (usually goes into the wall).

An S trap is less resistant to having its water drawn out by a pressure differential in the drain. I'm pretty sure that S traps are no longer allowed by modern codes. You can still buy them as replacements, but it's not a bad idea to put in the extra effort to upgrade to a P trap.

Make sure your roof vents aren't blocked. Also check whether the sink is actually connected to the vent! I've seen older homes where the roof vent served only the toilet.

If it turns out that yours isn't connected, adding an air admittance valve (if your code allows them) is going to be less headache than tying the sink drain in to the existing vent stack.

Judicious use of chlorine bleach won't damage a septic tank that's regularly used and properly maintained. Just don't overdo it. That said, I see no particular utility in dosing the drain with any kind of disinfectant.

Thank you David! When having this house renovated post purchase, much of the bathroom was gutted and the sink I had installed is one I bought new some years before and was waiting to use (American Standard Standard Collection Console sink with oval glass shelf.) Because the works underneath are totally exposed I bought the best chrome P-trap and fittings a local plumbing supply house had. In a month or so I'll have my plumber back to install a pump for my utility sink, and he will need to add another vent stack I believe, so I'll have him see if the sink is connected to the bath vent, and if the vent has any blockage. I'll ask him about the air admittance valve - thank you so much for that information!

Peroxide is less toxic than bleach and either one will react instantly with organic matter (alive or not) and be consumed. I don't think a bit of either one into a septic tank will harm it.

P-trap or S-trap, as long as it isn't dry why would sewer gas come up at all?

You can get under there and unscrew the sink trap and make sure it's not clogged up with some kind of gunk. Put a bucket underneath for the few ounces of water that will come out of the trap when you remove it. One should know how to do this procedure anyway, in case you ever drop a wedding ring in there or something.

I’m watching this closely as we are also experiencing sewer smell coming from sink in a 2nd bathroom, which is seldom used. The worst problem is that I can smell it but DH says he doesn’t. I applied a little Clorox once and it seemed to help but next time we visited, about 2 weeks later, smell was there but not as strong (or I got used to it). My wild imagination makes me think rodents or snakes could be trapped. Somebody please set my mind at ease, ha. But it doesn’t smell like dead animals. It smells like sewer.

could something like a bird nest clog the pipe sticking out of roof?

bossyvossy:

"...which is seldom used." Bingo. Your trap is evaporating, allowing the sewer gas past it. Run some water in your seldom used sink every week or so and your problems should be over.

Thanks....but...but....,It happens that it’s never been used regularly, so why the smell now?

For whatever reason, the trap is evaporating now and/or you're just noticing it now.

Before moving to this house full time we had that smell in the half bath when we got here. Running water in the sink made it go away. Now here full time no smell anymore.

Two years late but we are having the same problem with the double sink in our master bath and it’s a brand new house! Vents are clear and unless the gas can come through the faucet when the water is not on, I’m pretty sure it’s coming from the drains. When we stop the drains and leave water in the sinks we have no odor problems. Any ideas?

We are having the same problem with a new house. If you find the resolution, please let us know. Thank you.