Pour a half cup of salt, half cup of baking soda, and a cup of vinegar down the drain and let it sit overnight. In the morning, pour a pot of boiling water down the drain.
Hi Arlean, When I was a bar manager we had this problem because of the beer tap. I used hot shot no pest strips. They work like a charm. Here is a link to check it out.
Make sure you keep water in the drain. Many homes with a humidifier/dehumidifier dry up the water that blocks the sewer gases from coming thru in the summer. During the summer pour several cups of water in your basement floor drains. Pour some water and bleach in the drain and that should work like the p-trap under your sink does. Keeps the flies away and seals the pipe from gas.
All surfaces must be cleaned with solution of 1 part bleach 4 parts water. Drain, tub, faucets, counter tops, flooring... do this for 4 days and you will kill all the eggs. Repair any dripping drains. Put plugs on top of drains.