This is a small scale enterprise that UN-Habitat has been developing in Nairobi, Kenya. It is called 'Vacutug' and is a latrine emptying service.
The UN-Habitat site reports that the technology is "being constructed in association with a private-sector engineering company and a Kenyan water NGO. The micro-enterprise earned over US$10,000 over a two-year period and employed four people."
More details of the project can be found in this powerpoint presentation.
There are a number of reasons I like this business: the health and social class benefits of not using manual pit latrine emptying, the health benefits of proper sanitation, the rise in quality of life from proper sanitation, the market size due to the trend of urbanization, the need for the service is high density urban areas or squatter settlements where the walkways are too narrow for a regular sized tanker to reach, and the technology being specifically designed to be affordable and manageable for a microentreprenuer and the possibility for employment. Startup costs look to be around 5,000 per Vacutug.