Solids, effluent and scum (see illustration above). This, over time, turns into sludge. Septic Systems - De Pere - Green Bay - Appleton - Wi An underground series of perforated pipes flow under the tank itself. How does a three tank septic system work . Meanwhile, the liquid waste that ends up inside your septic tank rises to the top. The lighter solids, such as grease, oils and fats, rise to the top to form a scum layer. All the drainage pipes from your home are connected to the septic tank which forms the septic system. Septic tanks work by allowing waste to separate into three layers: After each septic tank, the lines converge and are led to a treatment and dispersal area. The incoming wastewater pass through three different rooms and while within lightest materials date back to flotation and heavier materials fall on the bottom of the tank. Since septic tank systems create an environment where there is limited oxygen in the wastewater, the septic aeration syst...