[mmr]

I have them terrible also. There are a few things you can try.
1)I take a old jar and put some fruit muched up in it, then plastic wrap the top with a rubber band. Take a tooth pick and poke holes all over. Set the jar by the cage (but so they can't get to it, birds I mean). After a few days that catches ton's of them. Throw the jar away and repeat if necesary.
2) I go to rural King and by their fly strips. They seem to do a great job! something like this, but the one's I get are all orange

https://www.ruralking.com/Store/detail.aspx?ID=27351

The flies breein in your drains from the left over sludge etc. Pour boiling water down the drains. That will help also!