Short answers, pulled from the story.
Archaeologists announced the discovery of remains from a 2400-year-old lavatory at the Yueyang site in Xi'an during February 2023. This ancient facility included broken parts and a bent flush pipe found among palace ruins by researchers from the Chinese Academy of Social Sciences' Institute of Archeology.
Scottish mechanic Alexander Cumming invented the S-trap in 1775 to seal the outlet of the bowl using standing water. His design prevented foul air from escaping the sewer while featuring a sliding valve in the bowl outlet above the trap.
George Jennings installed his Monkey Closets in the Retiring Rooms of The Crystal Palace as the first public pay toilets during the exhibition. Eight hundred twenty-seven thousand two hundred eighty visitors paid one penny to use them receiving a clean seat towel comb and shoe shine which led to the euphemism to spend a penny for going to the toilet.
Thomas Crapper did not invent the flush toilet but was in the forefront of the industry in the late 19th century holding nine patents including three for water closet improvements like the floating ballcock. In 1880 he introduced the U-shaped trap while his flush toilets were designed by inventor Albert Giblin who received a British patent for the Silent Valveless Water Waste Preventer siphon discharge system.
US Congress passed Energy Policy Act of 1992 mandating common flush toilets use only gallons per flush from 1994. Pre-1994 residential and pre-1997 commercial flush toilets typically used five gallons per flush while modern low-flush designs allow much less water per flush.