Drain flies


Old 12-24-17, 05:30 AM
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Drain flies

My daughter has a massive problem with drain flies at the kitchen sink. Thus far she's killed over 1,000 with homemade traps and a tape product. They've been using enzyme to clean the pipe. However, the problem seems to be getting worse and the flies seem to be broadening their range by a few yards.

My understanding is that the flies hatch and mature in the drain. I'm generally good at plumbing and my thought is to take out and replace the pipe between the sink and the "J" as I assume this is the source of the issue. That is, I assume the flies can't swim so the problem is confined to that area.

Any thoughts on this approach?
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Old 12-25-17, 07:28 AM
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At this point we have to assume that they’ve been identified correctly and are the type of drain fly that is also called “sewer fly” but technically named “psychoda”. They look like tiny moths as they are fuzzy. All of my advice is geared to this type of fly. There are other types of small flies that will live and breed in residential/commercial areas but their biology and the solution would be different.

Psychoda live and breed in stagnant water and/or decaying organic matter. Slow moving drains are oftentimes the culprit. Garbage disposals can be an issue here too. Do you have a trash compactor or a garbage disposal? Sometimes organic matter can be caught up underneath a flange or such and will not get cleaned out by usual cleaning methods/chemicals. Your idea of replacing pluming is good; at least take it off and inspect it. Another possibility is to get a water hose in the drain and flush hard. Just because cleaning agents are being used doesn’t mean the pipes are getting clean. Prior to that though, are you positive they are coming from the sink drain? If so, good. If not, take a clear drinking glass and spray/coat inside with vegetable oil/spray and invert over the drain. Must be a clear glass so that light shines through. If you find flies trapped within the glass then that confirms it.

One thing that is for sure with these guys is that wherever the densest population is, that is close to the breeding site. Examples of where I’ve found them: where sinks have been removed but exposed drain line not sealed well enough; behind/underneath trash compactors; underneath slabs where condensation/overflow line drains (bad practice); sump pump holes which have stagnant water in them but not enough to activate pump; dishwashers that aren’t used but still have stagnant water somewhere; broken/cracked sewer pipes in basements under slabs; broken sewer pipes just outside of the structure but underground; You get the idea.

The solution in practice is to remove or flush away the decaying organic matter and stagnant water. Sometimes that is simple other times not. Start with the simple stuff. Keep us posted as to what you find.
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