Yan Yu Lin and her seven-year-old daughter live in a tight studio in San Francisco’s Chinatown, in a century-old building where 60 or so residents on each floor share a bathroom.

Along the back wall of the room is a plastic potty – the kind designed for toilet training toddlers. The shared bathrooms are out of order so often, so rank and unhygienic, that Lin has her daughter use the plastic potty instead. “It’s safer,” she said.