a cross-sectional diagram of a septic tank, illustrating how it treats wastewater through gravity and biological processes. A septic system is the primary treatment stage for homes not connected to a centralized sewer line. It relies on a "settling" process to separate waste into three distinct layers. 1. THE THREE LAYERS OF WASTE As wastewater enters the tank from the home (on the left), it separates based on density: • Scum Layer (Greases): The top layer consists of fats, oils, and greases tha