I saw a mention of this on Global Voices and thought I'd point it out here. Rama, a social planner in Calcutta has an idea called the "Toilet Bus" that would bring portable sanitary toilet facilities to slums in the city by refitting an old double decker bus with the required plumbing. So far the idea hasn't been able to get rolling. Maybe one of our readers knows of people interested in this type of social enterprise? More from Rama:

I was seized by the idea of converting a decommissioned double-decker bus into a "Toilet Bus" to cater to poor women in slums like Priya Manna Basti in Howrah. Such a bus would be parked near the slum for a certain duration at particular times of the day. The refuse (which would accumulate in a safe storage tank in the vehicle) would then be disposed off at a dedicated land site, using a twin sanitary pit system. Once full, the pit would be closed and a new one used. When the second pit was full, the first one would be reopened. The refuse would be inert and could be removed and used as manure.

The toilet bus needn't have its own engine and driver-cab. It could be hauled and conveyed, with the cab unit conveying, parking and picking up a number of such toilet buses.

Besides giving immediate relief to a good number of poor slum women, this would also serve to highlight the sanitation issue and create wider public awareness of this problem. It would also be possible to organise the beneficiary women in self-help groups through this initiative. And this would serve as a demonstration of a programme that could also be taken up by others, including the municipal corporation.

The venture would be a non-profit one, but it would also generate revenue from user charges towards meeting costs.