One-chamber tank
Wastewater enters through the inlet tee. Scum floats, heavy solids settle as sludge, and liquid in between leaves through the outlet tee.
How conventional septic tanks work
Compare an open, one-chamber tank with a two-chamber tank. Blue arrows show the liquid flow, and tan particles show solids settling.
Two-chamber tank
Most solids settle in the first chamber. The liquid passes through a submerged opening in the divider, then leaves the second chamber through the outlet tee.
These are simplified side views. Tee dimensions and the shape and location of the transfer opening vary by tank design. Effluent leaving the tank still needs treatment or dispersal downstream.