Also, check if you have drain flies. They are very similar in size to fruit flies. Do you have any flies in your sink? If you do, pour a big pot (or two) of boiling water down the drain. That will do the trick.
Well, everything happens at once - our kitchen sink has a problem; we can’t use it or the dishwasher until they fix it tomorrow.
But we don’t really seem to have them around the sink. The trap that caught so many of them is quite a distance from the sink drain.