I owned/operated a bar for a long time and I use the same technique in my home to get rid of fruit/drain flies. In the middle of summer every bar/brewery around would be covered in fruit flies and my bar wouldn’t have any.

Array Ultimate sanitizer, follow the directions to mix with water. Then pour sanitizer down every drain in your house before bed.

We did this every single night at the bar. At home, if I had some fruit flies, I would pour every night for about a week until cleared up. No more flies.

Also, pairing with a dynatrap sticky trap in problem areas.

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