Ah don't be ashamed of not having known though. I used to work for a health department and did a lot of outreach in rural communities. It's amazing how little knowledge of wastewater systems there is out there. Education on private infrastructure is lacking. People might learn about public treatment plants (seriously Ms Frizzle's Magic School Bus is the primary common point of reference) and assume their house is served by the same: even when miles out side a city off a forestry road.