KARACHI: Late on a humid Sunday night earlier this month, four sanitation workers left their small homes in United Colony, a predominantly Christian neighborhood in Karachi’s Saddar Town, to do what they had done countless times before: descend into the city’s underbelly to clear blocked drains. By dawn, three of them were dead. The victims — George Masih, 43, his 16-year-old son Vishal, and their 18-year-old relative Sahil Khurshid — collapsed one after another inside a sewer filled with poisonous gas. Only Sahil’s younger brother, 14-year-old Raza, survived to tell the story.