Abstract: A septic system tank assembly, including a primary outer tank having a cylindrical wall, and within which there is nested a second tank also of a cylindrical configuration, extending diametrically across each tank is a dividing partition dividing the two tanks up into four chambers which carry out anaerobic, aerobic, clarification and disinfection treatment, the assembly further includes an air pump and conduits which delivers air to the aerobic chamber and a dispenser to dispense disinfectant material into the disinfectant chamber. The assembly also includes separate conveyor means to transfer both solid matter and floating matter from the clarification chamber to the anaerobic chamber.