Do you want a shockingly good read? Try Africa’s Infrastructure: A Time for Transformation (Agence Française de Développement and World Bank, 2010). There’s a chapter on sanitation Moving People Up the Ladder, and the chapter summary is:
A third of Africans continue to practice open defecation, and half rely on unimproved latrines, the health effects of which are largely unknown. Despite this sobering picture, progress has been made in recent years by individual households eager to protect their health and improve their quality of life. The immediate sanitation challenge differs depending on prevailing practice. Where open defecation prevails, the policy focus should be on hygiene education. Where there is already widespread adoption of latrines, the challenge is how facilitate upgrading to improved models. Where improved sanitation is already prevalent, the key question is how to develop low-cost sewerage in the most densely populated areas [emphasis added].
Quite. Get simplified sewerage into high-density low-income areas of African cities and towns and start doing so now.