Dec 08, 2016 - 02:48 PM
Other inside issues could be overwatered house plants, sewer issues, septic tank issues.
Otherwise it's an outdoor problem and they are getting inside. In this case, treatment of the lawn with Bifen IT could help. If you don't know where they are coming from, then using CB 80 and fogging the house periodically will also help.
We also have fly traps called Gold Sticks that work to capture drain flies and gnats. Do you know where they are coming from and how long has this been going on?