It’s a movie set in Australia, but not necessarily Australian. There was a group of weirdos living in a very strange house that looked like a castle made out of mud way far in the outback, maybe a swamp. There was a guy similar to Kevin Bacon riding a very cool bike. There was a scene where his character cuts off the Union Jack of the Aussie flag and replaces it with a red kangaroo in a blue field. It was from the late 80s, early 90s. Anyone has any idea?