How to get rid of drain flies
Drain flies are small fuzzy moth-like flies that breed in the slime layer inside drains and overflow tubes. They look like fruit flies but they're hairier and weaker fliers. Killing adults doesn't fix the problem — you have to scrub the slime out of the actual drain.
Tools
- ✓A 24-inch nylon drain brush is the key tool — chemicals alone don't remove the gelatinous breeding layer.
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Materials
- +The pro-grade enzyme drain treatment — what exterminators use. Pours in and dissolves the organic gunk over several days.
- +Alternative enzyme treatment widely sold in hardware stores.
- +Cheaper DIY: pour 1 cup baking soda, then 1 cup vinegar, wait an hour, flush with boiling water. Not as effective as enzymes.
- +Optional confirmation test — see step 1.
Steps
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1
Find the breeding drain
Cover suspect drains with duct tape (sticky side down) overnight. In the morning, drain flies will be stuck to the tape over the offending drain. Most often it's a rarely-used bathroom drain, a basement floor drain, or a kitchen overflow.
Tip: Don't skip this. Treating the wrong drain wastes a week. -
2
Scrub the inside of the drain
Remove the stopper, then push the drain brush in and twist hard against all sides of the pipe for 30 seconds. Pull out the brown gel that comes up — that's the drain fly nursery.
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3
Pour boiling water
Run a full kettle of boiling water down the drain to flush loose debris. Repeat morning and night for 3 days.
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4
Apply enzyme drain gel
Pour InVade Bio Drain Gel or Bio-Clean per the bottle (usually 4 oz at bedtime). The enzymes digest the residual film overnight. Repeat once a week for 2–3 weeks.
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5
Don't bother with bleach
Bleach kills adult flies it touches but slides right off the gel layer where the larvae live. Enzymes work because they eat the gel itself.
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6
Trap remaining adults
An apple cider vinegar trap with a drop of dish soap catches the last adults — but the cycle ends when the breeding site is dead, which takes about 5–10 days after scrubbing.