Go to a livestock store on line (I use American Livestock, and have for 20+ years). Buy a stinky jar, but the downside is you have to empty it, and it will make you barf. They have throw away bags that are great. They also make tops that you put on empty milk containers that are great and cheap. They come with attractant, however, put a fish head or raw fish piece in there, add water, start with an inch or two and set in the sun. It will attract thousands of flies. I have 2 outside right now. The problem may get a bit worse due to attracting more flies, but soon, it starts to cut down, and eventually you will have thousands less flies and their offspring. Every few days or so, swish it around, and keep the water about 1/2 inch above the dead flies. Flies are attracted to the stinkiest stuff around. Dead flies make the pukey bad fish water smell even worse. It helps alot to keep all other things that attract flies to a minimum so the containers have less to compete with. These are great. You will be suprised how fast they fill up, and full is 10,000 flies or more. Raw fish is the best, and at least you are not feeding the nasty pesty maggot layers.