Resource people in local economies are those with RVs that understand holding tanks, etc.

Gray water is all of the wastewater that drains from your shower and kitchen (click here) and bathroom sinks. Gray water has some bacteria but it can be filtered and reused in gardens or lawns, if done properly.

Black water contains human waste and is unsafe. It must be stored in its own tank and disposed of very carefully...

These concepts are similar to what occurs on a much, much larger scale with regular sewage treatment.