How to Get Rid of a Musty Smell From a Tub Drain

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If you notice musty bathtub drain smells, take a look at the bathtub drain and there's a pretty good chance you'll see blackening around the drain strainer, which is a sign of mold. Even if you don't see any discoloration, the chances are still good that there's mold in the drain because it's the No. 1 cause of musty smells.

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We're not talking about sewer smells; those are a different thing with different causes. A sulfurlike smell from a bathtub drain, which is characteristic of sewer gases, isn't just musty — it's downright malodorous, and the main reason for that is a dry P-trap. That means that water has been siphoned out of the P-trap, and that usually happens because of a clog in the vent pipes or the waste line.

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Musty and Stinky Bathtub Drain Smells

If you want to solve your odor problem quickly, you need to distinguish between the musty smell of mold and the downright stink of sewer gas. To identify musty, think of going into a wet basement or opening a trunk that has been locked tight for years. The air you breathe feels like it lacks oxygen, and it may even smell slightly smoky. The smell is subtle but unpleasant.

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That's different from the noxious smell of sewage, which is full of such gases as methane and sulfur dioxide. It makes you wrinkle up your nose or hold it, and if the smell is strong enough, it can even give you a headache. The smell has a certain pungency that suggests you could light the air on fire, and if enough of the gases were to collect in the bathroom, you actually could. Humans have a natural aversion to both musty mold smells and noxious sewer gas odors, but the reaction to sewer gas is stronger.

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How to Get Rid of Musty Smells

If your nose tells you that the smell from the bathtub is musty, you're dealing with mold, mildew, and bacteria in the drain. The microorganisms tend to collect around the drain opening, so removing the tub strainer and cleaning around the drain opening with baking soda and water should help. One effective way to scrub is to soak a mini paint roller sleeve in a vinegar solution and swish it in and out of the drain.

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Mold and mildew also grow on hair that has collected in the drain, and you can fish that out with a Zip-It tool, which is basically a long cable tie with notches. After removing the hair, give the drain the old baking soda/vinegar treatment. Pour half a cup of baking soda into the drain and follow with a cup of white vinegar. This creates a cleansing foam that will overflow from the drain. Let it work for about 15 minutes, pour hot water into the drain, and the smell should be gone.

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My Tub Drain Stinks — It's Not Just Musty

If the odors coming from your tub drain smell like sewer gases, you have a dry trap. This probably happened because you don't use the tub often, and the immediate fix is to pour water into the drain to fill the trap. That should stop the gases from wafting into your bathroom for now, but you need a longer-term fix.

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The No. 1 cause of dry traps is blocked vents, and if that's the problem, you may notice smells from other drains, or you may hear gurgling sounds from the sink or tub drain or even the toilet every time you pour water into a drain. You may also notice that drains empty slowly or the toilet doesn't flush completely. Check the vent opening on the roof because it may be blocked. Ice is a common cause of roof vent obstruction, and it isn't unheard of for birds and small animals to build nests there. If you can't find any problem when you check the roof vent, call a plumber.

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