It's supposed to refer to when you dispose of your garbage on someone else's pile. From the wording, I guess it's as if you're giving a "tip" to the flies feasting on the trash.

The theatre/cinema thing.

A theatre is a place of public entertainment where a cinema is a place to watch films.

A theatre can more easily be used as a cinema than vice versa.

I'm more taken with the film (pronounced fillum) v movie thing.