The problem of open defecation is one that needs to be dealt with and I think it takes more than just SMEs to make this work. The Nibbler and Gulper are appropriate to help at the household level. The scene in the Slum Dog Millionaire however seemed to show centrally located latrines serving tens of thousands of people in a single location. I have been thinking that for such cases, given the problem of legality, difficulties with construction and displacement what might be needed is a system where the latrines are installed in such a way that they feed directly into a tanker trucks that could be moved emptied several times a day. Cities or private individuals could buy say a dozen 30,000 liter tankers with maybe 3 tractors that would just make the rounds and empty these tankers at treatment plants, or even better combine the collection with large bio-digesters that would help with local energy provision and produce concentrated natural fertilizer that could be sold to farmers/gardeners. One would need to develop a logistical system that ensures that the latrines are always available and reasonably clean and the waste is systematically picked up and recycled. I could easily imagine a PPP with the company operating such a system generating revenues in part from a subsidy by the town, part payment by users, and in part from the sales and distribution of electricity and high value fertilizer. These systems work for pig farms in Denmark, Germany and Holland, I am not sure why this could not work in underserved large concentrated communities. You could even add an incentive, and have a yearly redistribution of proceeds to the participating communities based on the volume of waste collected, or maybe free electricity, whatever, one would have to think of the modalities.