A septic tank is an underground chamber used for the treatment of wastewater from homes and buildings. It is typically made of concrete, fiberglass, or plastic and is designed to hold sewage long enough for solids to settle at the bottom, forming sludge, while lighter materials like grease float to the top, creating scum. The treated liquid, known as effluent, then flows out of the tank into a drain field or leach field, where it is further filtered by the soil. Regular maintenance, such as pumping out the sludge, is essential to ensure the system functions properly and prevents environmental contamination.