If you are not familiar with terra preta, it is the name for meters thick black soil found around inca dwellings.
Their sanitary system consisted of doing their business in a clay pot and throwing a thin layer of biochar on afterwards.
When the pot was full it got delivered to the soil people who broke the pots and scattered the broken down compost and loaded biochar into places they needed to convert to an arable soil.
That whole area is covered in terrible clay soils that are not suitable for farming. What they did to convert it was nothing short of a miracle, and the best part is the biochar will serve that soil for thousands of years. Sadly it is being exploited by people digging it out and selling it.