Do slow drains mean septic problems?

Water circling down a stainless steel kitchen sink drain By winnond/Shutterstock

My kitchen sink and bathroom sink drain very slowly to the septic tank. There is no issue with the toilet or the shower drain. The septic tank has been checked and the baffles are clear. Any thoughts on what might be causing this slow drainage? Could the problem be because of a venting issue?—Slowly Going Crazy

It could be, yes. Assuming that each fixture is vented separately, the vents from the kitchen and bathroom sinks may have been installed improperly—pipes that are too small, have too little or too much slope, or are located too far from the traps. Or maybe the plumber didn’t install vents at all. “We have a joke about plumbing in cottages,” says Matt Girard, the owner of M&J Plumbing in Peterborough, Ont. “It follows ‘cottage-country rules.’ Sometimes the hardware store is a little far away,” he says. “You gotta MacGyver it.”

Signs and symptoms of septic failure

According to Max Burns, the author of Country & Cottage Water Systems, another possibility is that an individual vent stack is blocked by, for example, a bird’s nest. (Look on your roof.)

If the sinks aren’t vented or are vented incorrectly, they’ll need a plumbing rejig to fix the draining problem. That’s a job best left to an expert.

But, wait—lack of venting may not be the cause of your slow drains, says Burns. He suspects that the traps under the individual sinks are clogged. (Traps, with their U-shapes, are common spots for blockages.) Newer plastic traps have a clean-out plug at the bottom, but older metal ones may not. To loosen and dislodge the gunk, you’ll need something like a long bottle brush, says Burns. Stay away from chemical de-cloggers. “I would not put drain cleaner in any system that’s on a septic,” says Burns. “It kills all the good bacteria.”

You’ve already got plumbing problems. No need to create new ones!


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