good humane way to put them down all at once - get your car cranked get you a pipe and a trash bag....stick the cage in the bag, duck tape it to the fitting pipe then set the pipe over the tail pipe (i reccommend a second pipe so as not to let the plastic trash bag come in contact with the tail pipe...
Then come back in 20ish minutes and they should all be dead and you can throw them in trash, bury them, whatever disposal means you chose. You are not poisoning them and you aren't being 'hands on' in their termination. Many folks do this with foxes and raccoons that they can't legally shoot because of gun laws
Wow, that's a lot of rats! Makes me wonder how many you really have around your place if you caught this many in one night. I agree with finding a friend who has a snake to feed. At least, that way, they don't go to waste.