Psycho was the first film to ever show a toilet flushing.
Alfred Hitchcock’s 1960 film Psycho captivated audiences and is one of the go-tos when people talk about the invention of the slasher genre. It was, for certain, a film of firsts, and one of those firsts just so happened to be the first time a toilet was seen flushing on the big screen! (On TV, the first episode of Leave It to Beaver in 1957, was the first TV program to show a toilet, sort of. In the episode Captain Jack, you could see shots of a toilet tank, but not the toilet itself. The first time we heard a toilet flush on TV was during an episode of All in the Family, in 1971. )
The Haus of Dcaligari 