Most certainly know what is going on with those flies. Trapping is your best option. The fly bait trap you used got filled in one day. That may sound like $6 down the drain,,,,,,,,, BUT THERE ARE OTHER OPTIONS. You can reuse part of it to make you own home made traps. You can also reuse the liquid and use as bait in trap after you empty it. That is what I do.
I pour off liquid,, (yes it is smelly) into a disposable container. Empty the rest of the dead flies into sewer drain. Return liquid into bottle, and add whatever water to create flies drowning.
You can purchase bait only, and also some one way trap tops, to install on one gallon plastic bottles. Those are available at most Farm, and Feed Stores. I like using apple juice bottles because they are clear. Flies see other flies inside, and cant wait to get inside.
DE will not do much to control flies. It is more effective on crawling insects that may be inside your coop litter bedding.
Here are some pix of what I use.
WISHING YOU BEST,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, and
