A proper septic system is carefully engineered but they can still be quite low tech. Many houses still just have gravel trenches and pits.

My own home doesn’t have any pumps, it just pushes water out as water comes in. My tiny strip of land has deep trenches and the right native soil (deep sand).

More modern systems just need some pressurized lines and only three feet of the right sand to achieve proper treatment of effluents.