How can I get rid of house flies?

There are special made fly traps now that you can special order or buy that are made for kitchens such as yours, or even patios to trap the pests. They are one way traps you empty each day. Also, I would begin by locating the attraction to make so many flies come. Do you live in an agricultural area? If so, you have no control, but if a neighbor or someone is failing to pick up the yard after their dogs or garbage etc, that may be something you can control by talking to them or reporting them so your neighborhood is not so attractive to flies. Also there may be improvements you can make such as better screens or a screen door etc you can add to your home.

Other than using a swatter, you really need to locate the source of their entry. Clean up everything outside where maggots might be (warm, wet and organic). Next, keep them from coming in. Mix up a spray bottle of water and clove oil. Two cups water and about 1 tsp clove oil and/or cedar oil. It will be strong smelling, but flies HATE it. Spray around the outside of all doors and windows near the kitchen. Next, check all the weatherstripping and door sweeps to make sure there are no gaps. Replace if needed. Also, check any screens you might have. If any are worn, they'll come in that way, too. Hope that helps!

Lots of tips here: https://www.craftylittlegnome.com/flies-house-suddenly/

We used a gallon sprayer (https://amzn.to/2Qcr66m) and sprayed on organic Pyrethrin (https://amzn.to/2Cz9QWe).

In a small glass bowl, I mixed hummingbird nectar with a small squirt of dawn dish liquid, a little powdered sugar and if you have it banana extract. I've made it without the extract and it works, it just takes longer to attract them. They come to the liquid and then the dish liquid makes it so they can't fly out.

Here's a post that might help https://chascrazycreations.com/irish-spring-soap-and-flies/