Read the introduction by Greg Kotis in the published script. The idea came about on his trip to Europe, when he decided to extend his stay and ran out of money. Having encountered mostly pay toilets, he had to become creative in ways to relieve himself and in Paris, he came up with the title and underlying theme of the show and decided immediately it should be a musical. Upon his return to Chicago, he met with Mark Hollman, provided a very rough synopsis of the show and after three weeks, Mark returned with "It's a Privelege to Pee". Over the next three years, the show was developed.
So there.
"What can you expect from a bunch of seitan worshippers?" - Reginald Tresilian