We had a small invasion of flys this weekend, about 20. Wife says "outside flys OK", "inside flys must be killed". Once the fly comes in the house, the death warrent is signed. I can't let it out as it must be killed. My technique? Wait until it gets dark, turn off all of the lights except for the bathroom. When the fly goes into the bathroom I close the door, grab a can of Lysol and give it a quick spray. I then take a tissue and pick up the dazed fly and flush it down the toilet. All nice and clean. Wife is very proud of me. She says I am expert fly killer.