Phorid flies will breed wherever moisture and organic matter are available.
Sorry, just burn the house....
Or like i said, till the frass till its dry. You just gotta get rid of dead things for about 30 days and keep the bin dry. So 24 hour rotation of any veggies etc. maybe a small pc fan blowing into the bin.
FLy traps near a light, above the bin will work too. Remember only flies can lay eggs, no flies, no babies.