...which brings up a good point. Most musicals don't mention or feature such things (or the use of them), though we can assume they DO exist in each show lol. But a few do --
Toilets - Urinetown (duh), Billy Elliot, Avenue Q, 1776. I suppose we could include (indirectly) Chicago ("I gotta pee") and Lucky Stiff (the song "A Woman In My Bathroom"). Maybe the washroom scene in How To Succeed? (I can't be sure I've ever seen a production that had more than just a row of sinks and mirrors - never any toilets lol.)
Toothpaste - South Pacific (Pepsodent), On Your Toes ("You have lost that bright toothpaste grin"). I don't recall that Orin Scrivello, DDS ever mentions toothpaste, however.