Why does bleach not get rid of drain flies?

Because bleach and other thin liquid cleaners flow past the gelatinous biofilm lining the drain without dislodging it, and that film is where the larvae actually live and feed. Killing a few larvae on the surface doesn't remove the habitat, so flies keep emerging. The fix is mechanical: scrub the pipe walls with a stiff brush to physically break up the film, then follow with an enzymatic cleaner that digests what remains.

How do I find which drain is breeding the flies?

Tape a piece of clear tape sticky-side down over each suspect drain opening overnight — any flies emerging from that drain get trapped underneath by morning, confirming it as the source. Test every drain in the affected area, including ones you rarely use, like a basement floor drain or guest bathroom sink, since biofilm builds up fastest where water sits stagnant. Once confirmed, focus your scrubbing effort on that drain.

How long does it take to get rid of drain flies?

Scrubbing a confirmed drain takes under an hour, but full resolution usually takes a few days to a week as the enzymatic cleaner finishes digesting any remaining biofilm and existing larvae complete their life cycle. If flies are still present after a week of consistent scrubbing and enzymatic treatment, recheck for a second breeding drain you may have missed, since flies can be developing in more than one location at once.

Are drain flies dangerous to my health?

No. Drain flies are weak fliers that stay close to their breeding drain, don't bite, and carry no documented disease risk in a home setting. They're a pure nuisance — mildly unpleasant to look at, but not a threat to you, your family, or pets. The correct response is straightforward sanitation and drain cleaning, not alarm. If you have respiratory sensitivities, heavy mold or biofilm buildup in a neglected drain can occasionally trigger irritation independent of the flies themselves, which is one more reason mechanical scrubbing is worth doing regularly.

Daniel Brady · NH-Licensed Pesticide Applicator · License #782664

How to Get Rid of Drain Flies

DIY-friendly

To get rid of drain flies, physically scrub the gelatinous biofilm lining the inside of the breeding drain, then follow with an enzymatic or microbial cleaner — pouring bleach or spraying insecticide doesn't work because both largely miss the water-resistant film larvae actually live in. First confirm which drain is breeding them with an overnight clear-tape test: tape a piece of clear tape sticky-side down over the drain opening, and any flies emerging get trapped underneath by morning. Once confirmed, use a stiff, bent-wire brush to scour the interior pipe walls below the drain opening, then apply an enzymatic cleaner over a few days to digest what remains. Drain flies are weak fliers that stay close to their breeding site and pose essentially no health risk — this is a pure nuisance fix.

At a glance

Difficulty: Beginner
Time: Under an hour per drain, plus a few days of enzymatic follow-up
Cost: Low — a drain brush and an enzymatic cleaner
Success: High once the correct drain is identified and physically scrubbed

The honest answer

Can you DIY Drain Fly?

The verdict on Drain Fly DIY

DIY-friendlyBeginner

A beginner-friendly DIY — the fix is mechanical scrubbing, not chemicals.

Drain flies (moth flies) breed in the gelatinous organic biofilm that lines the inside of a slow or rarely-used drain. That's genuinely good news: the problem is a physical film you can scrub away, not a hidden colony you have to hunt down. Confirm the breeding drain with an overnight clear-tape test, scrub the pipe walls with a stiff brush, then follow with an enzymatic cleaner. No pest license or specialized equipment required.

The playbook

The 5 DIY methods — honestly graded

Every approach graded for this species, in IPM order — prevention first, chemistry late. Pick a method to see how it works, the steps, and what it actually takes.

Prevention / Exclusion

Works well

Identifying the exact breeding drain is the first step every other track depends on.

Drain flies stay close to the drain they emerged from, so confirming the source with a simple test focuses your cleaning effort on the right pipe instead of guessing.

Best for: Confirming which drain to treat before you scrub anything

Run the clear-tape test
Tape a piece of clear tape sticky-side down over each suspect drain opening overnight. Check in the morning for trapped flies.
Tip
Test infrequently-used drains too — floor drains, basement laundry drains, and unused bathroom sinks are common overlooked sources.
Keep drains flushed
Run water through infrequently used drains regularly to prevent biofilm from building up in the first place.

Tools & materials

Clear tapeFlashlight

Before you start

Don't skip the confirmation step — scrubbing the wrong drain wastes effort.

Reality check

Why DIY falls short here

Not scare tactics — the specific, proportionate reasons a home attempt can stall for this species.

Pouring bleach and calling it done

Bleach and thin cleaners glance off the water-resistant biofilm; larvae keep developing in what's left behind.

Treating the wrong drain

Flies stay close to their breeding site — without a clear-tape test to confirm the source, you can scrub the wrong fixture entirely.

Straight talk

How risky is it, really?

An honest read — most nuisance species are genuinely low risk, and we say so.

Low risk

Drain flies are a pure nuisance with no meaningful health risk. They're weak fliers that stay near their breeding site, don't bite, and carry no documented disease risk in a home setting.

Nuisance around sinks and showersCommon
Cosmetic and annoying, not hazardous
UC IPM / extension pest-management literature
Disease transmissionRare
Negligible in a residential setting
UC IPM / extension pest-management literature

When to call a pro

Drain Flies Keep Coming Back?

If scrubbing and enzymatic treatment aren't holding, a hidden plumbing issue could be feeding the problem. Anchor Pest Services offers full inspections across southern and central New Hampshire. Family-owned since 2017, NH license #782664.

Call a pro when…

Flies persist after scrubbing and enzymatic treatment on every drain in the affected area
You suspect a cracked pipe or broken seal feeding organic buildup somewhere inaccessible
You'd rather have a full inspection to rule out other breeding sources

General Pest Control

Most drain fly problems are a straightforward DIY fix. A pro adds value if flies persist after thorough scrubbing across every drain, which can point to a plumbing issue like a cracked pipe or a broken seal beyond a drain brush's reach.

Get a Free inspection (603) 785-0118

Keep them out

Run water through infrequently used drains at least weekly
Scrub drains periodically as routine maintenance, not just when flies appear
Fix slow leaks before they create standing organic buildup

New Hampshire context

Drain flies in New Hampshire homes

Drain flies show up year-round in NH homes wherever a drain sees inconsistent use — a basement laundry sink, a guest bathroom, or a floor drain. Warm, humid months can accelerate biofilm buildup, making a spring or early-summer drain-cleaning pass a good preventive habit.

Peak season

Warm, humid months, though drains can breed them any time of year

Before you treat

Make sure it's a Drain Fly

Two quick detours worth taking — confirm the ID, then learn what drew it in so it doesn't come back.

Not sure it's this?

Identify Drain Fly in the Pest Library

Why is it here?

What actually attracts Drain Fly

Common questions

Frequently asked

Sources & further reading(3)

[1]
UC Statewide IPM Program — Drain Flies
Biofilm biology and mechanical control guidance
extensionverified 2026-07-13
[2]
Southland Organics — How to Get Rid of Drain Flies
Enzymatic/bio-cleaner mechanism
industryverified 2026-07-13
[3]
Bahama Plumbing — Drain Fly Treatment
Mechanical scrubbing and extension-consistent guidance
industryverified 2026-07-13

Written & reviewed by

Verified

Daniel Brady

NH-Licensed Pesticide Applicator · License #782664 (NHDAMF, RSA 430)

Daniel Brady is the New Hampshire–licensed applicator behind Anchor Pest Services, a family-owned pest control company serving the Manchester area since 2017.

Verify license

Last updated July 2026

Other species you can tackle

Same category — the dot shows each one's DIY verdict at a glance (green = friendly, amber = doable with care, red = call a pro).

Fruit Fly

Fungus Gnat

Phorid Fly

Professional Pest Control

Drain Flies Keep Coming Back?

Get a Free inspection (603) 785-0118

NH-licensed applicators (#782664)
Free inspection — same-day service across southern NH

NH License #782664 · No obligation · We answer in person

Keep Exploring

How to Get Rid of Drain Flies

Can you DIY Drain Fly?

The 5 DIY methods — honestly graded

Prevention / Exclusion

Run the clear-tape test

Keep drains flushed

Why DIY falls short here

Pouring bleach and calling it done

Treating the wrong drain

How risky is it, really?

Drain Flies Keep Coming Back?

Call a pro when…

Keep them out

Drain flies in New Hampshire homes

Make sure it's a Drain Fly

Frequently asked

Other species you can tackle

Drain Flies Keep Coming Back?

Your next step

Pest Control Services

Drain Flies in New Hampshire — ID, Signs & How to Get Rid of Them

Drain Flies in New Hampshire — ID, Signs & How to Get Rid of Them

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What Attracts Drain Flies to Your House?

Mechanical Filth Fly Control: Find the Source, Not Just the Fly