Sir Charles Lavatory
His firm, C.H. Lavatory and Son, manufactures and markets the patented Lavatory device, which is a good idea in principle but hampered by the fact that Ankh-Morpork is yet to (re)discover sewers. His eponymous patented device cleans and flushes beautifully, but in keeping with the general miasma of Ankh-Morpork, not to anywhere in particular. Therefore if the house is nowhere near the Ankh and there isn't a dunnikin nearby nor space to dig one, the whole point is somewhat lost. Still, the Ankhian ethos of "once it's out of the house it's somebody else's problem" lives on. The person whose problem it is almost certainly works for Harry King.
The Lavatory device is fast replacing the earlier model patented by a previous Guild luminary, William de Privy. Perhaps the strangest client for the device was Death. The toilet in the house of Death has a pretty arrangement of green and blue flowers on the cistern.
Probably a reference to the Roundworld semi-hero that is Thomas Crapper about whom much legend has (incorrectly) been woven. Thomas P. Crapper was a plumber who founded Thomas Crapper & Co. Ltd. in London. Contrary to widespread misconceptions, Crapper did not invent the toilet, nor is the word crap derived from his name. This is indeed a pity, but he did, however, do much to increase the popularity of the toilet, and did develop some important related inventions, such as the ballcock. He was noted for the quality of his products and received several Royal Warrants.