First, gather some supplies. For this first one, I used an empty V8 bottle, some packing tape, and the bruised part of a pear. You can also use a soda bottle.Cut the top off of the bottle and take the lid off. Put the pear inside the bottle, then turn the top upside down and put it inside the bottle. I put some tape over the opening since it was a bit large. Don't make it too small though!Put tape around the top of the bottle to seal it, then put it somewhere where the flies are. Mine is right next to the sink.
Pour some cider vinegar into the bottom of the jar, and plug your glue gun in...
Make yourself a glass of chocolate milk while you wait for your glue gun to warm up.Once your glue gun is warmed up, glue around the inside edge of the jar, right at the top. Make sure the glue goes all the way around, no gaps!Press the funnel down into the jar immediately so that the glue will seal it off. I put mine on top of the litterbox in the bathroom. Hopefully this will eliminate the flies!!
UPDATE - After a few hours, I can say that the funnel trap is not as effective as the bottle ones, and that cider vinegar works better than fruit. 2 cider vinegar traps attract MANY more flies than one trap, even away from food. =)
UPDATE 2 - either I have smart fruit flies, or I didn't empty the traps quickly enough....I suggest that you empty them every 10-12 hours or so. I also have had some success with the vacuum....I use the traps to attract the flies to one area, then use the vacuum to suck the little buggers up. I WILL win this battle.