I'm just trying to help with this because I'm guessing I am not the only one who hasn't had some of the issues listed above. I found using a coffee filter poked with holes has made my kitchen science model free. I don't even measure, just pour enough apple cider vinegar to cover the bottom of my canning jar, filled with water and added a drop of my homemade dish soap. Then I covered my trap with a paper coffee filter, poked with a few holes with a toothpick and YEA!!! I set it out right by the fruit behind my "decorative" infusing vinegars (it sits where you dont even notice it) and showed my husband my brilliant solution to our annoying problem. He was wonderful and gave me that "oh, you are so cute" smile and congratulated me. Ah, whatever, I took it because I had finally beat the beast (ok size of a pin head isn't a beast but this is my blog, I had them EVERYWHERE).
Maybe I'm the only one with this issue, but if I'm not, I do hope this helps the next poor sap just trying to rid themselves of the oh so strangely cute, but irritating fruit fly.