I have heard all about these funnels and such for use with fruit in a bottle but i have found with vinegar or distilled spirits (plus a drop of detergent) there is no need to cover it at all, the fruit flies happily die right there and do not try to fly away. I had the oddest
experience, they didnt like the dry red wine i left them....shrug i went back to cider vinegar. I put it in a wine glass to keep evaporation down...any of the other methods seem right to me I will save a liquor bottle.
I wouldnt use the funnel method because I have a worm bin and need constant fruit fly control so I dont want what I leave out for them to look bad. A glass of vinegar near the worm bin and another in the kitchen next to the container i collect compost in (on another floor) does a great job of keeping them down (I rarely see one alive outside the worm bin). nagging my kids to rinse their soda cans did not work.