Vinegar to the rescue again
Dear Heloise: I recently moved into an apartment that had been vacant for several months. The one bathroom that I am not using has a tub that had a bunch of little fruit flies, and later, small flies. I later learned that they were sewer flies. I filled the tub with water a couple of times and used a container for the fruit flies that I got from the hardware store. It did not work.
Source: texarkanagazette.com