>I had always assumed Thomas Crapper himself to be a myth
Neither myth nor inventor (or post Minoan re-inventor) of the flush water closet. There had been a number of attempts. of varying succes, to provide water-carried sanitation before Crapper. He is well known because he perfected a flush system invented by others, which was further refined over the nineteenth century. The main problems that beset Crapper's system was that it used an inordinate amount of water, in a time when water supplies to cities were not very good, and the valve was prone to stick, which meant that even more water was used.
If you really want to find out all about it, read
WRIGHT, Lawrence, (1960) "Clean and Decent: the fascinating history of the bathroom and watercloset" Routledge.
A very well written and interesting book which will tell you all about the debate over whether earth closets or water closets were best.
