I've been battling a fly problem for about 2 months. The flies stay mostly in the bathroom and kitchen so it definitely has something to do with the drains. At first my wife and I thought they were fruit flies but we have come to the conclusion they are "drain flies."

I've tried cleaning out all of the drains, flushing it with boiling water and applying some type of gel to coat the pipe...It's not having any mitigating effect really. The best thing we have been able to do is keep out jars of vinegar mixed with soap. The flies get trapped in the suds and die. The only problem there is we are just killing the adults and the problem still perpetuates.

I've inspected the septic tank and it seems normal...apart from the hundreds of flies that make their way out when I open the lid. I'm thinking they are breeding in the tank and finding their way into the house up the drains. You would think the p-traps would stop them but I am starting to worry there is an issue there. Could it be the case that the drain in the shower floor doesn't have a p-trap? Should it? I've checked the plumbing vents - there are three - for any blockages and there are none.

There is a PVC T connection at the end of the inlet into the septic. One direction drops into the sludge tank and the other points up above the water level...would it hurt to block the upward facing part of the T? I feel like that is the flies best entrance into the plumbing. All of the cleanouts are sealed and clean. I've considered just draining the whole tank with a trash pump and letting it dry while I go on a bug free vacation. These flies are pissing me off.

Any ideas?

Check the overflow drain in your bathroom sinks. Sometimes they can get going in there.

[This message has been edited by the fife (edited 4/22/2014 8:42a).]

No overflow in the sinks...the tub could be a culprit.

I figure it will be something really obvious and I will feel like a simpleton afterwards. Thanks!

Wait... Your sink has no overfill holes? Never seen one like that before.

It's an antique copper sink. My wife doesn't like anything easy to find and/or install.

my late father described himself as a country boy and over and over said he knew those country flies had just been on wet, warm cow manure...Daddy would lose it, go almost insane if a fly was found inside our home and certainly within the kitchen!

If I had flies in the numbers you are talking about...there would be no cooking until we found the source and eliminated it! Check your trash cans, don't leave them under your sink!

It's a tiny fraction that actually make it into the house. I think my wife would bug bomb the house everyday otherwise.

Do you have any plants inside of your house ?

If so then it's probably fungus gnats/ fruit flies


Get the plants out of the house and put straight vinegar in every p trap in the house at night.

Every drain has a p trap. Well, it SHOULD. AS for the sink, not all have overflows. A lot of mine do not.

Try covering the tub drain when not in use and see if the flies stop coming in.


You know, the flies will disappear if you stop pooping. Eliminate the food source and they won't bother you anymore.