We have been trying to be rid of "sewer flies". We were putting enzyme down the drains, and in the end we felt like that did not have an effect. We put oiled cups over the drains too, without success. Finally, we agreed to keep the drain stoppers closed, and even thought to tape off the overflow holes. We have had very few in the house now after combating them all summer. However, we are seeing them outside on our doors. After all of this, we are beginning to wonder if they were coming in from outdoors in the first place or if it is the end of their season. Do you have any information on these sewer flies that will help us eliminate them?
The insect looks like a drain fly. We do not think they are coming in from outside. Once it freezes they will be gone.
The flies breed in water and the larvae are aquatic. They breed in drains.
Indoors you will have to eliminate breeding sites. Look in bathrooms and unused bathrooms too. Flush every now and then.
Use enzyme cleaners in drains. You can also try drain cleaners for hair and grease sporadically. Look for ones that foam as they get into tight places.
See our page for more information https://extension.umd.edu/hgic/topics/drain-flies