Last year one of my sons had a rat problem around his chicken coop. He killed quite a few rats and the problem lessened. One of the ways he killed them was to bury a garbage can in the ground and place a piece of plywood with a hole cut in it over the opening. He then put some chicken feed in the bottom. The next day there were fifteen rats trapped in the can. He then filled the can with water and drowned the rats.
Since then he has killed more rats with this method. You have to wait a bit between uses. Recently the rats have came back and he has started trapping rats again. I think his kids got a bit careless with the chicken feed. Over the winter, the garbage can had been removed and the hole filled in. Now not wanting to have to dig another hole, he set the garbage can upright on the ground and put a 2×4 leaning against the can to make a walkway for the rats. A bit of chicken feed in the bottom and it is catching rats. He is using an old plastic garbage can and surprisingly they have not chewed their way out. He checks the can and drowns the rats when he catches them.
This method won’t always work. Rats are smart and will stay away for a while after he traps a few. But after a few days some of them seem to forget. In an emergency since there is no poison or pellets involved this is a good way to get some eating rats.