pintu: a lot of people say it's a rotten job, but i don't agree. we also clean toilets with our bare hands. how else can you do it when they're blocked? this work is our bread and butter. reporter: and it's dangerous. oxygen levels can be low in large cesspools. last year, some 300 sewer workers died in india from drowning, suffocation, or exposure to toxic gases. the more privileged social classes prefer to ignore the dalits' plight. they're invisible to most. in india's more than 3000-year-old caste system, the dalits are the lowest of the low. even today, 70 years after discrimination on the basis of caste was officially banned. with no chance of upward mobility, it's hard for people like ashok to maintain even a semblance of dignity. it's 10 degrees celsius, and he has to wash out in the street. ashok: i have to soap myself down two or three times to get rid of the stench. and to make sure i don't get sick with all the bacteria. i've often had skin rashes. reporter: dalit activist bezwada wilson is waging a campaign against this deep-rooted dis