I made a new version of the fruit fly trap, seems more effective in killing, instead of just trapping.
Jar with an inch of apple cider vinegar, put 3-4 drops of liquid soap in the vinegar. This breaks surface tension and makes the mixture like quicksand.
Cover top of jar with plastic wrap and poke a few holes in it to allow flies in. You don't have to put plastic on if you don't want, but if you don't, they some times just collect on the rim of the jar instead of going exploring past the plastic to find Allah.