My BIL is a plumber....he says the worst thing you can do is to put hot grease or oil down the drain. If you have to do it, run it with cold water. It keeps the oil from infiltrating and building up as much.
The other thing he says is this: There’s two things you gotta know to be a plumber 1) sh!t flows downhill, and 2) DON’T bite your fingernails!