I used to live near the horse barns at the NC fairgrounds. Flies were horrible in the summer and the old rental house I lived in had way too many places for flies to get in. I used to get them with a regular shop vac. It had enough suction to pull them right out of the air if you got the hose anywhere near them. I’ve never seen a fly vac but if it’s got suction like a shop vac it should work great