i use WD-40. kills em in a few seconds. i know that if you set a jar full of gasoline out it will attract and kill all sorts of bugs, flies included. or you could get a bunch of duct tape and put all over the outside of your house sticky side out. or go out there with a vaccuum cleaner and go to town. a flamethrower would be great. you could get one of those cattle prod things and place the electrodes really close together and zap em one by one. get an army of chemeleons(sp?) and let them loose on to the flys.
ok ill stop now
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drew