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Tracking down a sewer gas smell... any tips?

David Meiland

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Just what I needed! Customer reports an intermittent strong smell of sewer gas in or near the downstairs bathroom... and outside somewhat near the septic tank. This is a seasonal house, empty for weeks or months at a time during the 8-month off-season, and heavily occupied during late spring and summer. My presence is not generally desired when it's occupied and I have not smelled it myself.

I went out there with my plumber and his sewer-cam. He scoped the line from the downstairs bathroom to the tank and pronounced it intact and unblocked (of course, no one had flushed in a long time). He also scoped from a cleanout near the guesthouse to the wye with the house line, and pronounced that OK also. His is a camera that needs 3" or larger, so there's a lot he can't inspect with it.

On the same trip, he checked the downstairs toilet and determined that the wax seal was probably broken, pulled the toilet and found it was definitely broken, and replaced it. His feeling was that this was the indoor problem. This guy is good and I believe him.

I've been involved in a few other deals like this. In one brutal case, we capped everything and blew smoke into a roof vent with a re-purposed bath fan and a smoke bomb from the fireworks stand. That helped find an open pipe in a wall that was causing a stink.

We haven't yet looked at the outside issue--septic inspector is next up on that one.

These folks want absolute certainty. We can smoke test, fill everything with water, perhaps get a camera that does smaller lines. I'm afraid of false negatives, obviously. Any other ideas?

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This is not a situation where traps are dry. It occurs when people are staying there and using all of the fixtures. I'm more inclined to suspect volumes of water down the drain that are either disturbing the sludge layer on the top of the tank, displacing air from the tank and waste lines and causing it to enter the house somehow, etc. Jim, what have you found in your investigations, if not sewer gas?

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For some reason, people think that every strange smell must be sewer gas.

And I thought people considered every strange smell to be that of natural gas.

Any chance there's a leaking propane tank nearby? You'd probably smell that one. Or maybe an aldehyde smell caused by incomplete combustion of something? Just trying to think outside of the box.....

My best idea would be to have the owner put you up for paid "vacations" so that you can experience the smell yourself.

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