In many countries, particularly developing ones, onsite wastewater systems remain an important measure for sanitation management. The poor situation of onsite sanitation systems is a common phenomenon in both developed and developing countries. The fundamental issue of onsite systems is that they are not considered to be a public matter, and, since many people do not care about them, they are not even a private matter. Thus, onsite sanitation is “no person’s land.” This case study discusses how to make onsite systems a public matter at each step of the sanitation service chain, taking Japan’s onsite system, which is very much a public matter, as a reference. To improve the onsite systems in other countries, it may not be necessary to use the same framework as the one in Japan; it must be one that reflects the unique situation of each country. Having said that, the framework in Japan would be a useful reference for any country that wants to improve its onsite system.