Sewage-like smell in kitchen that comes and goes

NewEnglandSaraNovember 8, 2013

Hi All,

I am hoping that you might be able to help us with an issue we are having in our kitchen. (It is driving us a bit nuts!) :-) We moved into a new construction home almost two years ago, but the house is on the original basement foundation. The basic gist is that we have a sewage-like small in our kitchen that comes and goes. Sometimes it smells as if it is coming from our main sink, sometimes from our prep sink and sometimes from an in-between spot. The dishwasher itself smells fine, and we have checked the filter in there on a few occasions. When we first called our plumber, he suggested dumping some bleach down each sink drain. We tried doing that a few weeks ago, but the smell still seemed to come and go. At first we thought it was worse when we ran our dishwasher, but more recently it seems to happen randomly. It might be worse on hot days, but we aren't sure. My husband checked for mice, etc. in the basement and underneath the sinks, but he didn't see any sign (and we have never had rodents in the past....) In addition, we have a second bad smell that is coming from our center island (where the prep sink is located.) That spot has a musty odor that is like our basement smell, but my husband thinks this is separate from the sewage-like odor.

A bit of background...Since the house is super tight/energy efficient, we had some early issues with mold in the unfinished concrete basement. We had to toss all of the wood/organic items down there and buy a super strength dehumidifier plus clean the space. We then had some issues with a main sewage line back-up into our basement, but we had that snaked in early September (and it has been fine ever since.) Since the house is so super tight, we decided to put in two ERV systems (heat recovery ventilators) to bring in fresh air. Those were installed in early October, and it is possible that the smell coincides with when those were installed. We had the ERV guys come back to take a look, but they said that everything was sealed up tight. (We do have a vent that comes out right underneath our main kitchen sink.)

Today we called back our plumber, and he told me to try three things: put citrus in both garbage disposals, wipe out both garbage disposals and run Pine Sol (diluted in warm water) through our dishwasher. I will try these things, although I would rather use vinegar than Pine Sol in the dishwasher. (Would this be similar?)

We welcome any input from the wonderful GardenWeb community. We are feeling uncertain about who can help with this smell, and we don't want it to cause any toxic issues for our kids.

Thanks so much,


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I would call another plumber. Get a second opinion about the sewer gas. It's coming from someplace and you've got to find it. Do you have an old washing machine hookup that's allowing the gas to enter the home?

    Bookmark   November 9, 2013 at 7:22AM
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If you didn't have the odor until the ERV system was installed, then I'd be suspicious of that. Is there any way to shut down the system to see if the odor disappears? One would assume the vent in the kitchen is removing stale air, not bringing in fresh so my first question to the ERV people would be 'what is the purpose of the vent under the sink'.

If the ERV is the culprit, you still have the issue of where the odor is originating from.
As the other poster suggested, bring in another plumber who's willing to do more investigating of all your plumbing lines and vent stacks.

In a previous home we had a sewage odor between a guest bed room and the master bath room. A plumber discovered the vent stack in the wall wasn't connected.

    Bookmark   November 9, 2013 at 1:20PM
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You have many dynamics here so you need to break them down and eliminate them one by one.

IâÂÂm assuming the vent under the sink is a supply vent (the kind that pushed out cold and hot air). If itâÂÂs an air admittance valve, I have seen those allow sewer gas in when not working properly. An AAV allows air into a drain line where a traditional vent doesnâÂÂt work. These are very common on kitchen islands.

Go to the following site and see how and AAV is installed and then look under your sink to see if you have one. If you do, it may need to be replaced.

The ERV could be your problem but I doubt it. If the ERV was installed improperly where it creates a negative pressure in your home, it could be drawing in sewer gas. This contradicts how ERVâÂÂs are supposed to work so I doubt this is the issue. You would need a very large ERV to put an entire home under negative pressure.

Sewer gas is in your plumbing drain lines to the point of your sink traps or other fixtures. We have a soaking tub in our master bath that never gets used. Once that trap dries out, I get a pleasant reminder of sewer gas to run the water to refill the trap. That little bit of water in the trap keeps the sewer gas from coming in.

Let us know how it goes and maybe we can give some more feedback.

    Bookmark   November 10, 2013 at 12:08PM
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I suspect mepop is on the right track (and is way more experienced than me).

I was just going to add that if none of that works out, I have found that wastewater sitting in the dishwasher drain line can get funky if it sits several days. Usually I would only smell it when the machine pumps it out for a few seconds before starting the next load. So, after a load runs, I dump out any water caught in the clean dishes, close the door, let it drain into the sump for a couple seconds, then turn on the machine and let it pump for 5 seconds. That seems to get it pumped out.

However I still think you have a sewer gas leak or a clogged vent as mepop suggested.

    Bookmark   November 14, 2013 at 5:17PM
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My first thought was to tell you to check all traps to make sure you have water in all of them. I also think mepop is on the right track, especially with the AAV for the island sink.

Once I had a smell coming from my dishwasher that was driving me nuts. I discovered that when I had replaced my disposal I hadn't secured the discharge hose into a loop as kind of a trap and apparently some gunk from running the disposal was managing to back up into that discharge hose and was causing the funky smell in the dishwasher. It doesn't take much to cause a big stink. Check all your traps, even the dishwasher discharge hose.

    Bookmark   November 14, 2013 at 6:48PM
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I would venture my best guess sewer gases are entering your dwelling. The only thing separating the sewer system from your living space is a few ounces or water in each trap, and a secure vent stack.

Somehow the methane from the sewer is bypassing your traps. I have seen vents that have enough occasional plugging due to a piece of roof shingle down the stack to cause enough back pressure to blow the water seal in the trap, not the same trap everytime.

I don't read where the plumber checked the main and secondary plumbing vent(s). AAV's fail regularly. Change it, they are inexpensive and simply screw on and off. Is it tight?

The big change you have is the ERV system. It is very possible it is bringing gas in with the fresh air somehow.

Mepop said;

The ERV could be your problem but I doubt it. If the ERV was installed improperly where it creates a negative pressure in your home, it could be drawing in sewer gas. This contradicts how ERVâÂÂs are supposed to work so I doubt this is the issue. You would need a very large ERV to put an entire home under negative pressure.

It may not be a negative pressure issue but may be bring in gas with the fresh air.

A new(qualified) plumber is a must to take a look at it. If you smell sewage open the windows, we don't want anyone especially the kids exposed, it can and will make them sick eventually, this are some very bad things in gaseous form here. Don't want to scare anyone but it is explosive if in enough volume. Learn about sewage gases.

Post this over on the plumbing forum and mention it's a cross post. This problem has been discussed before when I was a member over 10 years ago I recall.

Johnny D

Edit, copied from Wikipedia,

Sewer gases may include hydrogen sulfide, ammonia, methane, carbon dioxide, sulfur dioxide, and nitrogen oxides. Improper disposal of petroleum products such as gasoline and mineral spirits contribute to sewer gas hazards. Sewer gases are of concern due to their odor, health effects, and potential for creating fire or explosions.[2]

Lets definitely rule out sewer gases first, then rest assured there is plenty of time to find the source of the odor.

This post was edited by SouthernCanuck on Fri, Nov 15, 13 at 0:38

    Bookmark   November 15, 2013 at 12:27AM
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Wow, I can't thank everyone enough for these thoughtful replies. The crazy thing is that we haven't noticed the smell since I wrote the email! However, it was so strong off and on for several weeks. Any sense of how we could explain that? In the meanwhile, we will follow up on these great suggestions and report back! :-)

Thanks again,


    Bookmark   November 15, 2013 at 12:59AM
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"I would call another plumber. Get a second opinion about the sewer gas. It's coming from someplace and you've got to find it."

I agree with this.

Do you have a fireplace or use gas appliances? I have heard that crumbling chimneys or cracked vents can allow noxious gas to enter.

A link that might be useful:

    Bookmark   November 16, 2013 at 8:48PM
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It may have many a reason why the odor is no longer present which is great,from a dry trap in any sink drain or due to a dry drain going from the basement to the city sewer. I didn't mention the basement drain of which I was remiss to do so. These drains are often the culprit as they don't see any fresh water added to them unless there is an overflow onto the floor, a good amount at that.

If anyone has a basement drain to the town sewer systems add water to them a few times a year at least so they don't go dry due to evaporation.

    Bookmark   November 19, 2013 at 2:57PM
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I'm having the same problem as New England Sara right now. I smell is coming out of my kitchen sink. Like Sara, it comes and goes. I checked all the connections under the sink and even went down to the basement to check the sewer line and everything looks good. I suspect a bird built it's nest in the vent which is in the roof above my kitchen. I set up a bird feeding station outside my kitchen window so I can see the birds. Unfortunately, the roof is in the same general area. Only one way to find out.

    Bookmark   August 29, 2014 at 2:32AM
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You can't play around with potential sewer gas. The stuff can be deadly. Get a plumber.

    Bookmark   September 3, 2014 at 5:47PM
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Garbage disposals do get smelly form time to time; years ago an apartment manager advised us to try running cold water into our disposal while adding dishwashing liquid detergent (not dishwasher machine soap), then to stop the water and let the disposal suds up a bit...this works really well if the problem is in the disposal unit itself.

Worth a try, as it is very simple to do.

    Bookmark   September 5, 2014 at 4:24PM
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To help clean inside upper rim of garbage disposal use a new toilet bowl brush right size for the opening. Dawn or other dish cleaning soap will work great for this purpose. (Keep toilet brush for this purpose only).

Slimy Crud accumulates under the deflector flap over the opening. Some machines have removable deflectors and others do not.

    Bookmark   September 6, 2014 at 4:05PM
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