It’s hard to make a living as a waste picker. In Dar es Salaam, Tanzania—where most trash ends up illegally dumped—waste pickers spend up to 12 hours a day walking around the city, collecting and lugging other people’s garbage in long plastic bags. It’s a valuable service for the city, which doesn’t have a recycling program. But it doesn’t pay very well. In a day, a full-time waste picker might make less than $1.50. A…