The first flushing toilets were invented in the 1500s, and the first “s” shape modern ones were invented in the mid-1700s. A sewer system to connect them to, and the typical person using them instead of dumping a bucket into a cesspit, took until the mid-1800s.
It took multiple major cholera epidemics, and, more importantly, The Great Stink of London making the Parliament building smell bad, to convince London to adopt the technology. And, after that, the rest of the world.
One issue, for example, is miasma (bad airs) theory, the thought that airs created disease. By that thinking, connecting your home directly to public sewers seems like a bad idea. Add to that the problem of people still having cesspits that they connected to their new flush toilets to making poo-flooding a regular issue, and fear of the poor masses misusing or breaking them.
Sewer gas was a big problem in the nineteenth century when knowledge of how to trap the gas and prevent its return back into homes and city streets was scarce and workmanship in sewer construction often cheap and shoddy. Because of this at least one town in England, Manchester, converted from water-carriage to ‘the apparently safer and more effective dry conservancy method.’ A letter writer to the Herald argued:
A well sewered town may be described as supplied with a system of subterranean retorts, so arranged that the fluids in passing give off the largest volume of gases, which are carefully collected, and then by means of chimney pipes (for house drains serve admirably that purpose), conducted into the very heart of the dwellings.
The introduction of flushing toilets exacerbated the problem. The new toilets were gradually replacing the old chamber pots and used far more water. As a result more waste was being poured into the 200,000 cesspits that stored the capital’s sanitation. The cesspits would frequently overspill, contaminating the water supply and running human excrement into the Thames.
By the 1840s, London faced a sanitation crisis. One summer the stench of the Thames drove Parliament to soak their curtains in lime, an experience that led to funding for a modern sewer system.