Set up many many many traps and bait them with peanut butter. I had one exterminator recommend setting up 12 traps. If you're going to get the wood traps, get the ones with the yellow plastic trip on them and put enough peanut butter on it to keep the rat engaged.

I was going to get a 22 when we had rats, but, the misses didn't want me to miss and hit something I shouldn't,... like our water tank. Probably a good thing I didn't take the commando approach.

I remember my dad using his 22 single shot pistol. He bought bird shot for it so he wouldn't penetrate the roof. Well, it didn't penetrate the rat either.