100 years ago a typical working class family in a developed country had one adult spending their whole day cleaning
Hah, not my working class family. Everyone over the age of 12 worked sixty plus hours a week.
House cleaning isn’t a proxy for sanitation.
By the 1890s, flushing toilets were widespread and the first sewage treatment plant was built in 1865.
Nope. Back in the 1860s, toilets were extremely rare and households having their own water supply was even rarer. While cities like Liverpool had near-complete provision of WCs in homes by the 1890s, many industrial northern towns still relied on outdoor privies, with only 7.5 per cent of households having toilets in 1906 in towns like Rochdale. Even fifty years ago, in the 1967 House Conditions Survey found that 25 percent of homes in England and Wales still lacked a bath or shower, an indoor toilet, a sink and hot and cold water taps.
Many people still living recall shared outdoor toilets that served several houses/20+ people per toilet in some slum areas.
And that’s in England, a developed country, how do you think the rest of the less developed world was?
One sewage plant in 1865 doesn’t mean sanitation was good or widespread. China didn’t have any until the 1980s.