Septic systems are underground sewage disposal systems. They depend on bacteria, good soil drainage and regular maintenance to work properly. When you flush a toilet or drain a sink, the water enters drainpipes under your house and flows to the septic system.
In a typical system, the wastewater flows into a large concrete box buried in your yard. This is the digestion box. Solid material settles to the bottom while fat and grease floats on top of the liquid. Bacteria consume (digest) the organic matter and break it down. Bacteria reduce proteins to nitrates and starches to simple sugar and carbon dioxide. Whatever the bacteria cannot consume remains in the digestion box. As the liquid rises in the digestion box it enters a “distribution box.” This connects to drain pipes that are located in your yard. The “treated” wastewater flows through this drain field and percolates downward. It eventually enters the groundwater and moves away.