Banish Drain Flies Fast Using These Surprisingly Simple Tricks

If you’ve spotted these tiny, winged freeloaders humming around your plumbing lately, you know they’re small but stubborn. But don’t stress. We’re breaking down what brings drain flies to the party and how to send them packing (without losing your mind).

Here’s how two pros recommend clearing the clog and reclaiming your sink.

What Are Drain Flies?

Drain flies, also known as sink flies or moth flies, are tiny, fuzzy pests that love damp, gunky spots—especially the slime lining your drains. They thrive in stagnant water and organic buildup, making your kitchen or bathroom pipes the perfect hangout.  They reproduce quickly in warm environments, so infestations tend to spike in summer, especially in humid climates or poorly ventilated areas like older bathrooms or basements. 

Wizzie N. Brown, an extension program specialist at Texas AgriLife Extension Service, notes that it can be important to realize that adult flies only emerge from the drains; they don’t actually live there. 

“Rather, it’s the immature stage, or larvae, that live in drains,” she says. “They consume the organic matter that builds up.”

Drain flies don’t live long—just a couple of weeks—but they’re industrious.

“Eggs are laid by mated adult females in the slime layer of drains,” Brown says. “After they hatch, the larvae live in and consume the slime layer, eventually reaching about 1/4 of an inch.”

Larvae are wormlike, legless, and have a breathing tube that comes off the tip of the abdomen that they can extend to get air from whatever organic matter they live in. Translation? They’re built like tiny submarines, made for not just surviving, but thriving, in the muck.

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What Causes Drain Flies?

• Standing Water: Drain flies love water that doesn’t move—think leaks, clogs, or that guest bathroom that lies dormant between your sister’s visits. It’s the perfect place to lay low and lay eggs.
• Drain Gunk: That slimy buildup inside your pipes? It’s basically an all-you-can eat buffet for larvae.
• Drain & Sewer Issues: Gunk buildup can be exacerbated by drain backups and broken sewer lines, making broken pipes a common reason flies move in.
• High Humidity: Drain flies thrive in moisture-rich environments and humid air keeps moisture hanging around longer.
• Unused Drains: Sitting sinks and tubs can hold onto water and decay—ideal conditions for pests to party.
• Going Too Long Between Cleanings: When you skip cleaning, you’re basically rolling out the red carpet for drain flies. The longer the gunk sits, the harder they are to evict.

How to Identify Drain Flies

Unlike fruit flies, which gravitate toward produce and trash, or phorid flies, which love sewage, drain flies are devotees of damp, drippy drains. Chances are, if you have flies congregating near your drains, they’re drain flies.

For a more textbook check, Brown recommends placing a piece of tape over half of the drain before going to bed at night, or placing a clear plastic cup coated with petroleum jelly on the inside of the cup over the drain. Come morning, check the drains and look for small fuzz balls captured on either the tape or jelly that look similar to tiny moths. (Keep in mind, moths will have four wings—drain flies only have two.)

Drain flies’ fine hairs are actually one of their most defining features, and they also help explain the pests’ resilience. As Kait Chapman, extension educator of Urban Entomology at the University of Nebraska, explains, the fine hairs covering their bodies and wings give drain flies impressive water-repelling abilities.

“This adaptation allows them to survive in wet environments like drains by shedding water and avoiding drowning, making them much harder to eliminate,” she says.

How to Get Rid of Drain Flies

Daily Drain Maintenance

Keep things flowing—and fly-free—by running hot water down your drains daily and busting through any grub that’s collected on your drain entryway with a sponge.

Boiling Water

Up the ante by pouring boiling water down your drain, but keep in mind, that although pouring boiling water down the drain is a common and easy tactic, it typically doesn’t reach or remove enough of the sludge to be effective, Chapman says.

To do that, Brown recommends using a stiff brush to physically remove the organic matter build-up in the drain, then flushing the drain with boiling water. 

Baking Soda and Vinegar

Your favorite fizzy duo isn’t just for science fairs. Pour ½ cup baking soda followed by 1 cup vinegar, down the drain. Let it bubble, then flush with hot water.

Drain Cleaner

When DIY doesn’t cut it, bring in the big guns. Use an enzyme-based drain cleaner like Bio-Clean to quickly break down the buildup that drain flies feast on. Pros like Chapman prefer this method most.

“Enzyme-based drain cleaners are more effective than other methods because they break down and digest the biofilm that lines the drains,” she says. “For best results, we recommend pairing enzyme cleaners with physical scrubbing using a stiff brush to fully dislodge any remaining debris.”

Apple Cider Vinegar Trap

Set a homemade trap: Fill a small bowl with apple cider vinegar, cover it with plastic wrap, and poke tiny holes. Flies rush in but don’t rush out.