Years ago I lived on a pig farm and believe me there were tons of flies. We hung baggies half full of water in each door way or window that might be opened. They think it is a wasp nest & stay away. I know it sounds wacky but it works
I'LL TRY IT.
3 to 1 - apple cider vinegar and water
THANK YOU, I HAVE A SPRAY BOTTLE WITH 1: 1 SOLUTION OF WHITE VINEGAR &H2O FOR CLEANING MY WINDOWS AND IT WORKED.