How a Septic Leach Field Works: The Final Stage of Natural Wastewater Treatment This image illustrates the leach field (also called a drain field)—a critical component of a septic system that safely returns treated wastewater to the soil. While the septic tank handles separation and initial breakdown, the leach field is where final purification happens naturally, using gravity, soil, microbes, and time. 1. From Septic Tank to Distribution Box After wastewater leaves the home, it enters the septi