How to Get Rid of Drain Flies (DIY Guide)

Drain flies (family Psychodidae) are small (2–5mm), fuzzy, moth-like flies with large, leaf-shaped wings. They're poor fliers and tend to make short hopping flights, often resting on walls and ceilings near drains. They don't bite, don't transmit diseases, and are mostly just annoying.

Here's the deal: drain flies breed in the slimy biofilm that coats the inside of drain pipes. This film is made of decomposing organic matter, bacteria, and moisture — a perfect nursery for drain fly larvae. Each female lays 30–100 eggs in this film, and larvae can develop into adults in as little as 8 days.

The solution is simple: clean your drains. Remove the biofilm and you remove the breeding site. No chemicals needed.

• Drain brush or pipe brush — A long, narrow brush designed to scrub inside drain pipes. This is the most effective tool.
• Boiling water — Helps dissolve organic buildup.
• Baking soda and vinegar — A natural drain cleaning combo.
• Enzyme-based drain cleaner — Optional, for maintaining drains after initial cleaning. Enzyme cleaners eat through organic buildup without harsh chemicals.
• Tape — For the "drain test" to confirm which drains are the source.

Step 1: Confirm the Source Drain

You might assume you know which drain is the problem, but it's worth confirming. Here's the tape test: dry the area around each suspected drain, then cover the drain opening with a piece of clear tape (sticky side down). Leave it overnight. In the morning, check the tape — if drain flies are stuck to the underside, that drain is a breeding source. Test all drains in the affected room, including floor drains, shower drains, and sink drains.

Step 2: Remove the Drain Cover and Scrub

Remove the drain cover or stopper and look inside. You'll likely see (or smell) the slimy buildup where drain flies breed. Using a drain brush, scrub the inside of the drain pipe as far as you can reach. This physically removes the biofilm where eggs and larvae live. It's the single most effective action.

Step 3: Flush with Boiling Water

After scrubbing, slowly pour a pot of boiling water down the drain to flush out loosened debris and kill any remaining larvae. Do this carefully to avoid splashing.

Step 4: Baking Soda and Vinegar Treatment

Pour ½ cup of baking soda down the drain, followed by ½ cup of white vinegar. The fizzing action helps break up remaining organic matter. Let it sit for 15–30 minutes, then flush with another pot of boiling water.

Step 5: Check Less Obvious Sources

If drain cleaning doesn't solve the problem, check other potential breeding sites:

• Floor drains — Basement and garage floor drains that rarely get water can dry out, allowing flies to breed in the residual gunk.
• Condensation pans — Air conditioning units and dehumidifiers have condensation pans that can breed drain flies.
• Leaking pipes — Any area with chronic moisture and organic debris can be a breeding site.
• Dirty garbage disposals — Run the disposal with cold water and clean the rubber splash guard (the underside gets disgusting).

Step 6: Maintain Clean Drains

After the initial deep clean, maintain your drains to prevent reoccurrence. Run water through seldom-used drains weekly. Pour boiling water down drains monthly. Consider using an enzyme-based drain maintainer monthly, which keeps biofilm from rebuilding.

• Run water through all drains weekly — Even drains you don't use often. Stagnant water and dry traps are breeding grounds.
• Monthly boiling water flush — A quick pot of boiling water down each drain monthly prevents biofilm buildup.
• Clean drain stoppers and covers regularly — Hair catchers, rubber splash guards on garbage disposals, and pop-up stoppers all collect organic gunk. Clean them monthly.
• Fix leaks promptly — Chronic moisture from leaking pipes creates new breeding sites.
• Keep AC condensation pans clean — Check and clean your AC drip pan at the start of each cooling season.

• Pouring bleach down the drain — Bleach sits on top of the biofilm without penetrating it. It might kill some surface-level larvae but doesn't address the root cause. Physical scrubbing is far more effective.
• Using chemical drain cleaners — Harsh chemical cleaners (like the ones that "dissolve clogs") can damage pipes and aren't designed for the thin biofilm where drain flies breed. Stick to mechanical cleaning and enzyme-based products.
• Only treating one drain — Drain flies often breed in multiple drains. Check and clean all drains in the affected area.
• Confusing drain flies with fruit flies — If your "drain flies" are smooth-bodied and hover around fruit or trash, they're probably fruit flies, which need a completely different approach. Drain flies are fuzzy, moth-like, and stay near drains and walls.