Environmental Concepts by Ken & Julie, 120 Pine Forest Dr, Aptos, CA 95003, US

A septic system is a highly efficient, self-contained, underground wastewater treatment system. Septic systems operate on a simple principal. Water in, water out. If you flush six gallons down the drain, six gallons will immediately leave the tank and travel to the leach field. Because miles of sewer lines are not needed, on-site systems are less disruptive to the environment. They are less costly to operate than the large municipal treatment plants and more efficient.