Domestic septic tanks do not work....they are a con!
A sop to the developement sector.
I am an expert on septic tanks, which worked perfectly based on bacterial digestion till the early sixties and the advent of detergents, high power bleaches, domestic water treatment with anti bacterial chemicals etc.
Septic tanks are now simply cesspits which require emptying annually.
Our countryside and river estuaries are being poisoned, because we favour housing developement over our health and the health of the sea around us.