John Harington described a flushing privy in 1596, but the device only became usable indoors when Alexander Cumming patented the S-trap in 1775: a bend permanently holding water that seals sewer gas out of the room. Joseph Bramah's improved valve closet (1778) and 19th-century mass-produced ceramic pans and cisterns made the fitting cheap enough for ordinary housing. Each closet, however, converted a contained cesspit problem into a continuous stream of diluted waste needing somewhere to go. Cities that plumbed closets into existing storm drains discharged them straight into rivers.
The water closet is the fitting that forced the sanitary city: it created the load that made trunk sewers, interception schemes and treatment works unavoidable, from Bazalgette's London after the Great Stink of 1858 onward. It also rewrote the dwelling plan, adding the bathroom, the soil stack and a per-unit water and waste connection that fixes minimum servicing standards and densities to this day.
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