Fly trap #1

In a small bowl add apple cider vinegar and a few drops of dishwashing liquid and leave at the source uncovered.
Fly trap #2

Fill a jar with a small amount of apple cider vinegar and a few drops of dishwashing liquid. Cover jar with plastic wrap and poke a few holes in it.
Fly trap #2 was supposed to be more effective, according to the website I found, but #1 worked much better. By the next morning only a couple rogue flies remained while the rest had drowned. The apple cider vinegar smells like rotting fruit, attracting the flies, while the dish soap breaks the surface tension so that when flies come to sit on the surface of the liquid they get sucked in.
Hope this is helpful to anyone else who is battling flies, especially with summer just around the corner and more fruit coming into season. I apologize for anyone who might be offended by the killing of fruit flies. I did give them a couple chances to leave on their own and anyone who ruins my sauerkraut is pretty much asking for war.
Anyone else have a better solution?