Bad smells from any drain in your house are nothing to ignore. If the odors are really bad – as in outhouse bad – there could be a problem with the plumbing system, particularly the vents. If the drain smells musty, like the inside of an old suitcase, an old pirate who comes to visit might exclaim, "Haahrr...thar be mold in them thar pipes."
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Both sewer gas odors and musty odors from mold can make you sick. The sewer gas problem might seem like the more difficult one to solve, but it could actually be quite easy, although the solution may involve a trip onto the roof. If a sink smells like mold, you can handle the problem with a couple of ingredients from your kitchen cabinet.
What to Do When the Kitchen Sink Drain Smells Bad
A malodorous drain can smell like a sewer even if it's just dirty because decomposing food smells like sewer waste. However, if you notice the same smell at a different drain, the plumbing vent could be blocked. When this happens, air can't get into the pipes to equalize pressure, and every time you flush a toilet or empty the tub, flowing water creates a suction that can empty sink P-traps.
The P-traps are supposed to be filled with water, and the water seals the sewer gases into the pipes. If the vents are blocked and suction is emptying the traps, there's a direct path from the sewer to whatever room the sink is in. Besides being smelly, sewer gases are noxious and flammable, so you need to do something.
When the vents are blocked, the problem is often caused by debris or ice covering the vent opening on the roof. If it's safe to do so, go on the roof, check the vents and clear whatever debris you find. If that doesn't solve the problem, the next step is to call a plumber.
The Sink Drain Smells Like Dirt
Organic matter isn't supposed to linger in the drain; it's supposed to go down the drain. However, hair, starches and congealed oils can gradually build up and prevent that from happening, and the result is a feast day for mold. Everything the pathogens, such as bacteria and mold, need to thrive is available in a drain filled with organic matter, including darkness, moisture and food.
Don't panic and try to clean the drain with bleach, which is bad for the pipes and can be dangerous if it lingers in the P-trap water. The best strategy, recommended by plumbers everywhere, is to pour a 1/2 cup of baking soda down the drain and follow this with a generous amount of a 50/50 solution of vinegar and hot water. The combination makes a cleansing foam that kills pathogens and loosens the debris so you can flush it away 10 minutes later with more hot water.
A drain that smells like mildew often has a buildup that needs physical removal. To do this, unscrew and remove the P-trap and clean out the vertical pipe attached to the drain with a long, thin object, such as an old chopstick.
Clean Out the Garbage Disposal
When a kitchen sink drain smells bad, the smell is often coming from the garbage disposal. An easy way to clean and deodorize the garbage disposal is to slice two or three lemons and grind them in the disposal. This treatment is even more effective if you fill the canister with ice first because the disposal takes longer to grind ice and lemons than it does just to grind lemons, and this gives the citric acid cleanser more time to work.
Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at Hunker and Family Handyman.