Hi coke71. Just came across your question and thought I could add something helpful to the answers you've already had. My dad used to tell me a joke - Q. How do you keep flies out of the kitchen? A. Poop in the hallway!!!!! Seriously though, it gives a clue to the solution! I take large jam jars (like the ones for cook-in sauces etc). Using an old screwdriver and hammer, I chop a square hole in the lid and turn the metal inwards to create a sharp lip. I then use garden wire around the neck of the jar to make a hanging loop. Then, the clever bit! I used to put a solution of vinegar and jam into the jar before hanging it, outside, about 10 - 20 feet away from where the flies normally enter the house. The flies go in but are too stupid to find their way out!
Now I have improved the chemistry because I want to attract flies rather than wasps - I charge the jar with a mix of bonemeal (garden store!) and water. The flies find this totally irresistible and hardly any come into our house now! Every now and then, empty out the gunge of flies and goo and recharge the jars. Problem solved! GOOD LUCK!