First off find and remove their food source. It may have started as fruit but they will eat just about anything that is soft. An easy way to tell is if you see their little larva on it.

Next, I used the yellow sticky paper with some success but if you are having a mass of them use a vacuum. It sounds strange but works great. They are too slow to out fly the suction. If They are resting on a surface come in parallel and about an inch above that surface. They can jump about an inch or two very quickly but fly slowly after that. After your first session go back about 15 minutes later and do it again. Repeat as much as needed.

Clean your drains out with lemon slices and cubed ice. Turn on the garbage disposal.

Did you also clean the sink overflow? I used a mixture of bleach, hot water,and a little dish soap to get rid of drain flies (frequently mistaken for fruit flies) last fall. I believe they came in on a potted plant that I had outside for the summer.