Hello, I really would like some help solving a sewer smell in my house. The sewer smell is sporadic. It hasn't appeared in a long while, then all of sudden it comes back. I have had the city (city water/sewer) come out and do a smoke test and there seems to be positive ventilation on all vents with no smoke entering back into the house. All of the toilets flush properly, albeit once in a while there will be a slight gurgling sound. All of the sinks drain properly. I had a plumber inspect the crawl space for apparent leaks. All of the sinks and toilets have proper traps installed and water in the traps. There is venting to all bathrooms and the kitchen. When the smell enters, I can also smell it from the foundation vents. Again, the plumber found no leaks or evidence of anything that could be causing the odor. What really gets me is that sporadic nature of the odor.

Any ideas or suggestions would be great!

This can be a tricky one. How did they do that smoke test? If you could pump smoke in from the city lateral and cover your vents on top of the roof that would be a good trick, it would also show you if you have a floor drain somewhere that you don't use and is now dry. That's a long shot but it does happen. The most common place for a floor drain is a basement or laundry room. If the trap on the floor drain runs dry you can get an odor.

Question: Do your "foundation" vents have caps ? Do you have floor drains in your house ? Do you have sewer ejector ? Do you have bathroom in your house you don' t use that often ?

darrel1953, thanks for the help. The smoke test originated from the clean out away from the house. Smoke billowed from the roof vents and no smoke under or in the house. We have 3 baths and are used daily. No floor drains. Oddly enough, the smell usually appears around 7-9PM nightly.

Milo, thanks for the help. The foundation vents do not have caps. No floor drains. Bathrooms used daily. No sewer ejector or pump of any kind. Gravity fed line to main about 180 feet away.

Dawgsnkats: Please, define for me "foundation vent" in more detail ? Is it a pipe sticking up from the ground somewhere in front of your house ?

Milo, foundation vents/crawl space vents the ventilation screens/vents that allow heat and moisute to escape from the underside of a house that does not have a basement.

Dawgskats: Oh, of course, I was thinking "plumbing". Sure, I am fully aware what those are. We call them "crawl space vents" here. That's why it didn't ring bells first time... :-D

If you smell sewer smell from crawl space, it is because there is sewer leak somewhere. Ground is saturated and as air flows from one side to another side, it moves it around... I would probably have somebody else to crawl there again and inspect it more thoroughly. Look for leaking tub/shower traps and kitchen sink drain line. Those leak quite frequently...
Let us know what you've found out...

So what regularly happens at your house around 7-9 PM? That is, do you run the dishwasher, clothes washer, someone take a shower, give kids a bath?

Srtoud, man I wish I could get my 13 year old son to take a bath at a regular time. The timing is what is the weidest. No baths at or after water is run. No more washing of clothes at 7 than at noon on a Saturday. Dishwasher usually runs while we sleep or first thing in the morning. I have even closed bathrooms for days to ensure that they aren't the problem.