Plumbing trap dry or defect causes sewer gas odors in the building (C) Daniel Friedman Hard-to-Find Sewer Gas Odor Source FAQs
Q&A on Odd or Unexpected Sources of Sewer, Septic or Sulphur Odors

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Tracking down septic or sewer gas smells:

How to find mysterious sewer or septic smells when the source is not obvious. This article suggests things to check when you have had trouble finding the source of a sewer gas, septic gas, or methane smell in or near a building.

Sometimes the odor source is elusive because it comes and goes, is weather dependent, fixture use dependent, or because the leak is in a building wall or ceiling cavity.

Start with the inexpensive and easy things like checking for dry or defective fixture traps (or fake traps as shown in our page top photo).

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Tips for Tracking Down Hard-to-Find Sewer Gas Odors in buildings

Septic odors from vent pipe (C) Daniel FriedmanThese questions and answers about finding unexpected sources of sewage, septic, or sulphur odors in buildings were posted originally at SEWAGE ODOR SOURCE LOCATION - please be sure to review that article.


On 2018-11-04 by (mod) - batteries can be a sourece of sulphur-like or sewer-like odors


Thank you very much for this helpful field report of another possible source of sulphur odors ("sewer gas odors") that we had not previously noted: a failing battery such as often found on battery-operated sump pumps and other battery backup systems.

I'll be sure to add your example to our list of unexpected sewer odor sources found at SEWAGE ODOR SOURCE LOCATION.

On 2018-11-04 by Anonymous

I had a plumber come to my basement because of a smell of sulfer (rotten eggs) in the basement. It was getting stronger. We tried looking at all the sewar lines, boiller, etc... He found the smell. It was the the emergency battery on our sump pump.

Either the battery was bad, or the charger was overcharging the battery. Once we removed the battery, the smell disappeared.

On 2018-10-04 by (mod) - venting system problems can cause sewer odors


That sounds to me as if there is a problem with the venting system for the bathroom drain or its fixtures. Ask your plumber to review the details and connections of how the fixtures and drains are vented.



On 2018-10-03 by Amy miano

Hello, I had my bathroom updated about a year ago. Soon after there was a sewer smell that radiates up out of the sink drain and intensifies greatly when the water is turned on and the gas is displaced upward.

Cleaning the slime out of the drain helps for a day or two and then it comes right back. I have flushed the toilet to see if the water in the p trap moves, suggesting a vent issue, but it does not.

There isn't any gurgling noises. I'm guessing there must be a venting issue but the smell isnt anywhere else in the house, only this sink drain. How can I figure out how to fix this? Thank you

On 2018-08-05 06:50:40.301559 by Darren

Thanks. Will try that

On 2018-08-04 14:51:32.474001 by (mod) -

Sounds as if you need a plumber to do some pressure testing of the drain, waste, vent piping to confirm that there's a leak, then inspect for dry traps, or for incomplete or improper venting that might be backdrafting into the home.

On 2018-08-04 07:48:03.024590 by Darren

Recently moved into a renovated house that hadn't been lived in. All new plumbing in house.

Noticed a sewage like smell in hallway which is above basement bathroom where soil pipes leave house to connect to very deep main drain.

All the soil pipes in the house come together below hall floor from upstairs bathrooms. Drain service people found no blockage or obvious leak and were puzzled . Smell seems worse in morning. Not obviously worse when it rained recently. No sign of water on basement bathroom ceiling or where we can see pipes behind access panels.

Seems worse after upstairs bathrooms used which makes sense given pipes from there go under hall floor. But if no leak or blockage then don't understand smell. Extractor fan from basement bathroom under that floor too but vents outside and no obvious smell by outside vent. Any ideas ?

On 2018-08-03 16:12:05.169048 by (mod) -


There is no cinnamon test that serves as a widely-applicable odor source test.

There are several test procedures that release an odor source (such as cinnamon oil) inside of the heat exchanger of a forced air heating furnace as a (not entirely reliable) test for furnace heat exchanger leaks.

Cinnamon as well as other odor sources are also used in some medical test procedures.


we describe an inexpensive method for testing specific materials or surfaces to determine if they are the source of an odor in or around a building


we organize a variety of tools and approaches to tracking down odor.

One needs to match the odor test or tool or detector to the type of problem being addressed.

For example one might use a combustible gas detector to sniff at drains, plumbing fixtures, toilet bases, etc. for sewer gas leak sources.

Often the proper starting point includes interviewing building occupants, noting relationships between odor presence and activities, time of day, etc. See the home page I cited as the best place to start.

Research on Odor Source Identification

Start at the home page I cited above.

Additional scholarly citations are below:

Research on Subjectivity in Odor Strength Opinions

On 2018-07-31 08:54:06.485293 by Amy

What is a cinnamon test to diagnose where odor is coming from

On 2018-05-19 01:21:50.436499 by (mod) -

Let's start by mapping the relationship of the room to what Plumbing fixtures are nearby underneath above or alongside.

If it's a bathroom I would start by cleaning the surfaces. If it's not a bathroom I might be looking for a reason that we have a sewer gas leak and warm weather. I might also look for some or other heat induced odor sources.

On 2018-05-19 01:02:17.017553 by smith

Hello, first off, thanks for the chance of asking a question. Hope to get your help.
One of my room has sewer smell in the summer, but not in the winter. The totter the weather, the stronger the smell.
It should not the sink's P-traps since they are clean. What you suggest to do?

On 2018-05-02 14:29:19.516339 by At My Wits End

So the comments about the septic tank would not cause any of what we are experiencing with inside odors??

On 2018-05-02 14:11:25.822709 by Anonymous

So the comments about the septic tank would not cause any of what we are experiencing with inside odors??

On 2018-05-02 14:09:01.026593 by (mod) -

Usually the condition that you described is caused by a blocked or missing Plumbing vent system. Ask your plumber to check that out.

On 2018-05-02 14:03:34.718841 by At My Wits End

We have a terrible sewer gas smell that starts coming up from the drain as soon as I start letting the water out of my tub in master bathroom (lower level, high off ground). There is also a standup shower in this master bathroom that tends to have a faint smell of sewer gas after taking a shower.

When the sewer gas is happening in the master bathroom I can also smell it coming out of the drains in my kitchen sink. We have one other bathroom on the lower level of the house (lower to the ground) that never has had any type sewer gas smell. Note that our backyard tends to hold A LOT of water when it rains. This was an existing house when we bought it 5 years ago. It was built in 2005.

We found out that another house was on this property in the same spot but burnt down. We were able to find an inspection of the septic tank when the house was rebuilt that stated that the septic tank lid was caved in and the outlet tee needed to be installed.

We assume this happened when heavy equipment rode over the top of it when clearing the burnt home.

The only records we have show a new septic tank lid was installed. Nothing states anything was done regarding an outlet tee.

We have had a plumber come out and check plumbing vents and those are fine. Also inspected that no signs of methane gas are coming from toilet. Please, please, can someone please tell me what they think is our problem. I'm ready to sell and get out.

I cannot take the smell of sewer gas any longer or I'm going to lose my mind.

On 2018-04-27 19:41:20.146010 by (mod) -

I would clean and disinfect the sinks and surrounding fixtures.

On 2018-04-24 22:05:24.476353 by Sandy

We smelled sewer odor that lasted about 2 weeks in our master bathroom. Odor is gone, but we now have drain flies that originate from one of the two sinks. A plumber did a video inspection and a smoke test, but found nothing. This is only a 2 year old home. We are not sure what to do now. Any suggestions would be appreciated.

On 2018-02-05 22:37:03.871353 by Andrew Hurt

We have a septic system and there is an odor that comes from an air vent in a room in the basement. Technically, it comes from around the duct work at the vent opening. A camera snake and 3 smoke tests were inconclusive.

We had 2 of 5 wax rings replaced to no avail. The smell is the worst when anything upstairs such as shower, washing machine, or dishwasher is used.

We’ve been in the house for five years and the smell has gotten more persistent. It might go away for a day, but it always comes back.

Any ideas? Any questions?

On 2017-11-27 00:00:28.757467 by (mod) -


Sounds to me as if you need a plumber who can provide a drain clearing service. I'm experienced drain cleaner can often feel the nature of the obstruction on till you if there's also a problem with a broken or collapsed sewer pipe. Otherwise I would send the sewer camera down the line

On 2017-11-11 07:57:31.931972 by Pd

Hi, 2 story home about 11 years old. Upstairs toilets (qty) clog often and overflowed slightly couple times when clogged. Both upstairs tubs have slow drain. Sometimes both toilets gurgle.

Off and on and rare bad sewage smell in these bathrooms but gone within hours or next day.. Have laundry room upstairs with no real issues we know of. Down stairs toilet only clogged 3x in 2 yrs but did overflow slightly 1x during a clog.

No sink issues except gurgling noise sometimes when toilet flushed. Kitchen has garbage disposal. Starting smelling bad odor and musty going up staircase sometimes.

Now out of nowhere, 1st time ever, master upstairs br double vanity sinks water smells sulfur bad. Seems to only be at night and only noticed 3x in last 2 weeks. Next morning it's gone. Also that pipe thing on roof was installed upside down.. we left it. Haven't checked for clog yet.anyideas?

Scared major septic issue? Oh tried max Drano in tubs and no help. Thank u so very much

On 2017-08-08 01:38:42.037597 by Mark (sour smell in bathroom)

6 month old new construction on an aerobic septic system. Upstairs bathroom has a strong sour smell after a shower or bath is taken in one of the other bathrooms on thAt side of house.

Smell is always in the same bathroom.

Plumber replaced wax ring on toilet today but smell came back after shower was taken this evening.

Smell is not constant and shows up after a lengthy shower or large bath is taken. Water has been poured into all drains. Problem started about 3 months after moving in. Suggestions on next steps?

On 2016-03-05 14:15:54.545309 by (mod) -

Sewer gas may smell like sewage, rotten eggs, sulfur. Pee odor is more likely from a loose toilet, un-flushed toilet, or a thoughtless pee-er with poor aim.

On 2016-03-05 04:05:59.166012 by Josephine

Please discribe the smell. I smell pee then it smells like chemical.


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