Psycho was the first American film to show a toilet being flushed onscreen!

Though the toilet was never credited in the movie, our sources tell us that its name was ‘John’. Sadly, our porcelain friend was only given one line: “FLUUUUSH!” when Janet Leigh’s character was shown disposing of a torn-up piece of paper in it. It’s glorious debut was also upstaged a few moments later by the shower.
(source)