Drain Flies: Remove the Slime They Breed In
You get rid of drain flies by cleaning the slimy buildup inside the drain where they breed. Sprays only hit the adults that you can see. If the flies keep coming back, the problem is deeper in the pipe, and professional drain cleaning can clear it for good.
This post covers where drain flies come from, the steps that work, and what to skip.
Where Do Drain Flies Come From?
Drain flies are small, fuzzy, gray flies with moth-like wings. You often see them on bathroom and kitchen walls near a drain. They are also called moth flies.
They lay eggs in the film of grease, soap and food that coats the inside of a drain. According to Iowa State University Extension, the larvae feed on that organic slime. Fixing the source is the only real cure.
Where to Look
Check the drains you use least first. Floor drains, basement sinks, spare bathrooms and laundry drains are common homes. A drain with standing water in the trap, or one that has been slow, is a likely breeding spot.
They Multiply Fast
Adults live about two weeks. Eggs hatch in a day or two. A new fly can grow from egg to adult in one to three weeks, so a small problem turns into a swarm quickly.
They Are a Warning Sign
Drain flies do not bite. But they tell you that waste is building up in the line. A line that holds slime can also hold clogs.
Why Sprays Fail
A can of insecticide kills the adults in the room. It never touches the larvae living in the pipe. New flies hatch in days, and you are back where you started. Iowa State notes that household insecticides give only very temporary relief unless the larval source is removed.
Why a Dry Trap Matters
Every drain has a trap that holds a little water. That water blocks sewer gas. In a drain you rarely use, the water dries up and the pipe walls stay damp and dirty. Flies love that setup.
What Are the Steps to Kill Drain Flies for Good?
Follow these steps in order. Do them every day for a week to break the cycle.
Step 1: Find the Drain
Tape a piece of clear plastic over each suspect drain at night, sticky side down. In the morning, check for flies stuck under it. The drain with the flies is your target.
Step 2: Scrub the Pipe
Use a stiff drain brush to scrape the walls of the drain and trap. The slime is thick and sticky. Water alone will not move it.
Step 3: Flush and Treat
Pour hot water slowly down the sides of the pipe. Then use an enzyme drain cleaner, which breaks down the leftover film. Follow the label on the bottle.
Step 4: Repeat and Watch
Run the cleaner again over the next few days. Keep checking with the tape. When no flies show up for a week, the breeding spot is gone.
Research backs this approach. The Ohio State University fact sheet says the best control is to remove the organic material in the drain. Utah State also suggests an enzyme cleanser to keep drains free of film. See the Utah State University guide.
Why Do Drain Flies Keep Coming Back in South Jersey?
If you cleaned the trap and the flies still return, the slime is farther down. Buildup coats the pipe past the part you can reach. A brush cannot get there.
Brothers Mark and Anthony Papaneri own and run The Sewer Kings, a family business built on the water and sewer trade they learned from their father. The crew is PSMA certified, licensed, bonded and insured, and handles calls across Evesham and the rest of South Jersey every week.
On many calls, a homeowner says the same thing. They cleaned the sink, the flies came back, and the drain is still slow. We run a camera down the line to see the buildup. Then we clear it with a cable or a hydro jet, which blasts the pipe walls clean.
What to Skip
Bleach and ammonia do not help. Iowa State says there is no benefit to treating drains with them. They run through the pipe too fast to remove the film. Sprays only give a short break unless you remove the larvae too.
Hydro jetting uses high pressure water to scour the full pipe wall. It clears grease, soap scum and slime that a brush and a bottle of cleaner cannot reach. For drain flies, that removes the food the larvae need.
Check Other Causes
Flies can also come from a leak or damp spot under a slab or in a crawl space. If you clean every drain and still see flies, call a pro to check the line.
When Should You Call a Pro for Drain Flies?
Call a pro if flies return within two weeks of a full cleaning. Call if more than one drain is slow, or if you smell sewer gas. Those are signs of buildup in the main line.
A pro can clear the whole pipe, not just the first few feet. Learn what hydro jetting is and how it works. Our guide on how often to clean your drains shows how to keep slime from building up again.
You can also stop the next round with better habits. Read what not to put down your drain. Grease and food scraps feed the slime. Running water in unused drains once a week keeps the trap full. Flies and a sluggish sink often share one cause, which why a bathroom sink drains slowly covers. Skip the bottle from the hardware store as well, for the reasons in what chemical drain cleaners do to pipes.
Ask the plumber to run a camera if flies keep returning. A camera shows heavy buildup, a cracked pipe or a spot where water sits. Each one can feed flies. Knowing which one you have saves you from guessing and wasting money on products that do not fix the cause.
Wondering how long a visit takes? See how long drain cleaning takes. Most homes are done in a single trip.
Frequently Asked Questions
Do drain flies come from the sewer?
Not directly. They breed in the slime that builds up inside your own drain pipes. Large numbers can come from sewer treatment plants, but most home problems start in a nearby drain.
Does bleach kill drain flies?
Bleach may kill a few, but it does not remove the slime where eggs and larvae live. It flows through too fast. Scrubbing and an enzyme cleaner work better.
How long does it take to get rid of drain flies?
Most homeowners see them gone in one to two weeks if they clean the source drain daily. If flies are still around after that, the buildup is deeper. The Sewer Kings can clear it for homes across South Jersey, including Evesham.
Still Seeing Drain Flies?
The Sewer Kings clears drain buildup for homeowners across South Jersey. Call us for a camera check and a clean line.
Call (856) 626-9366 today.