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Drain flies (Psychodidae) are the small fuzzy moth-like flies that appear in bathrooms and kitchens. They breed in slime inside drains. Here is the elimination protocol.
How to identify drain flies
- 1/8 inch long.
- Fuzzy, moth-like wings.
- Hold wings tent-shape over body when resting.
- Weak fliers; often hop or stay near surfaces.
- Active near drains, especially overnight.
Where they breed
Drain flies breed in the slime layer (biofilm) inside drains. Common locations:
- Bathroom sink and shower drains.
- Kitchen sink drains.
- Floor drains in basements and laundry rooms.
- Septic tank vents.
- Air conditioner condensate lines.
Find the source drain
Stretch tape (sticky side down) over each drain overnight. Check next morning. Drains with stuck flies are breeding sources.
Elimination protocol
Step 1: Mechanical cleaning
Use a drain brush to scrub inside the drain pipe and remove biofilm. Reach as far as possible.
Step 2: Enzyme drain cleaner
Pour enzyme drain cleaner (Bio-Clean or similar) into affected drains. Repeat weekly for 4 weeks. Enzymes digest the biofilm where flies breed.
Step 3: Boiling water flush
Pour boiling water down drains daily for 1 week. Disrupts biofilm and kills larvae.
Step 4: Trap remaining adults
Place small bowl of apple cider vinegar with drop of dish soap near drains overnight. Adult flies trap in solution.
What does NOT work
- Bleach down drains — kills surface biofilm but flies return.
- Foggers — adult flies in air; eggs survive in drain.
- Drain plumbers snake alone — does not address biofilm.
Verdict
For drain flies, enzyme drain cleaner + mechanical cleaning + boiling water flush eliminates the breeding source over 2-4 weeks. Always identify the source drain first; then treat consistently for full elimination.
Reminder: Always read product labels and follow safety instructions.