Cottage Q&A: septic odour in winter

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In the winter only, we get a septic gas odour in the bathroom. What’s causing this?
—A Little Nosy

“Odour is generally caused by poor venting,” says Jim Ripley, the owner of Turtle Tanks, a septic installer in Kelowna, B.C. Sewer gas is meant to stay in the pipes or exit out the vent stack on the roof. But winter can interfere with this process.

If you don’t use your cabin much in the off-season, it could be that a P-trap has gone dry, because the water in it has evaporated. No water means there’s no seal to prevent the gas from coming up through the drain and into the bathroom. The floor drains of shower stalls are prone to this, says Sandy Bos, the on-site sewage system inspector for Ontario’s Township of Muskoka Lakes. If a dry drain trap is the problem, the smell should go away once you start using the bathroom plumbing again.

Another possibility is that the plumbing vent stack is blocked by snow or ice. Unblock it, and you’re good to go.

Septic system and plumbing problems can be tricky to diagnose, and you probably don’t want to smell sewer gas all winter. If your DIY fixes don’t work, call an expert to investigate.

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