We've noticed gnats in the kitchen area daily with no source found. Recently my husband mowed over one of the septic tank cleanout 's lid that protrudes up out of the septic tank. It is still covered, but could this be the cause of our gnat problem? The septic tanks are working just fine, but these gnats seem be to coming from somewhere? We don't have houseplants. Just trying to solve the mystery.

Is the sewage piping open? Gnats also linger around fruit.

It's covered with a insulated faucet cover, so it's not the original lid. There is NO fruit anywhere in the kitchen. I'm stumped, never had this problem before. We've only had these cleanouts since we had work on the septic tanks a year and a half ago.

It needs to be closed, not just covered

We had this problem once the weather started to cool down a bit. And it is only in the kithen as well. I thought they were gnats, but from looking at them more closely and googling online, I think they are fruit flies. Although I have no fruit out in the open! But those type of flies can reproduce anywhere moist. So check your kitchen sponge, and under the sink to make sure it's not leaking. They also can reproduce in the drain. So I went and got Amonia and treated the drains (on the back of the jug it tells you how much to use for drains). This seemed to solve our problem :)

Depending on your location it is not always a requirement to seal the tank completely. In my area it is common to have a 4" PVC pipe in the yrad with 2 90 degree elbows at the clean out. However, if this was the problem the gnats would tend to stay at the tank opening. I think your gnats may be sewer flys. This site should give you a great deal of help. drain flies, moth flies drain fly control treatment

Bal nailed it with drain flies. My drains were infeswted with them also. Follow the treatment suggested in the link he provided to get rid of them. Drain flies live in your drains and get into ypur home from there. Good luck, Tom