Regarding rats, i had an interesting similar experience a few years back, but with racoons, instead. My next door neighbor is the Queen Goddess Icon of hoarders. The house is not habitable, but my neighbor still owns it and lives in aretirement community. The house has become a giant storage locker, indested with rats, and mice, and racoons, and opossums, and probably a few brand new species of verimin to the planet. Well, those racoons ripped a long tear into our roof, unbeknownst to us, until it rained. My wife and i hired a live trapper to catch as many racoons as possible using live traps, and re,locate the critters to some other place outside the City. Good, we thought. We don't have to kill them to get rid of them. However, we subsequently learned that even if racoons are relocated, they usually always starve to death because their entire environment has changed, and what they've always learned about how and where to acquire food has gone poof! Take an urban 'coon and put it into the country, and there are no sewers, no trash cans, no compost piles, no food tossed out the windows of moving cars. They lack the abilities to adapt to a new environement fast enough to survive. That does make me feel bad about causing their deaths, but short of simply releasing them into someone else's neighborhood to continue to cause damage to other people's homes, what else is there to do?
Maybe if there was some oil involved, i'd feel better about killing the urban wildife.