Also the faeces have a long way to fall, which probably causes more noise and splashing than in wash-out closets. Nevertheless the wash-down is now by far the most common lavatory in Britain; so in Darwinian terms it must be the fittest for its UK purpose.
Disrespectful travellers have suggested that flush-out closets have a flat platform because the French and Germans are obsessive about wanting to examine their stools. In practice this design allows a sharp undercutting surge of water cleanly to remove even sticky excrement more efficiently than in any wash-down design. Furthermore the wash-out closet was patented in Britain by George Jennings in 1852, which is probably well before it appeared in Germany or France.
People seem to have been flushing lavatories with water for at least 4,000 years (see history), and the Romans had flushing latrines in England 2,000 years ago---although technically their latrines did not have separate pans---so it seems foolish to claim that the water-closet was invented by one particular person.
A self-contained water-closet was made by Thomas Brightwell of the parish of St Martin in 1449, but we don't know much about it, except that it was flushed by rainwater, collected in a lead cistern; see also the Abbot of St Albans. For the earliest one we do know about---1596---see Harrington.
Mira was hiding in the ladies' room. She called it that, even though someone had scratched out the word ladies in the sign on the door, and written women's underneath. She called it that out of thirty-eight years of habit, and until she saw the cross-out on the door had never thought about it. "Ladies' Room" was a euphemism, she supposed...
But here she was at the age of thirty-eight, huddled for safety in a toilet booth at the basement of Sever Hall... She was perched, fully clothed, on the edge of the open toilet seat, feeling stupid and helpless, and constantly looking at her watch.