The answer to 'what is septic tank' is a septic tank is an underground wastewater treatment system used in areas without access to a municipal sewer system. It is a key component of a septic system, which is a self-contained onsite wastewater treatment system for a home or business. The septic tank is where the initial treatment of the wastewater takes place before it is dispersed into the soil through a drain field.
Septic tanks are typically made of concrete, fiberglass, or polyethylene and are buried underground near the home or building they serve. They are designed to hold wastewater long enough for solids to settle to the bottom, forming sludge, while the lighter fats, oils, and greases float to the top as scum. The partially clarified wastewater then flows out of the septic tank and into the drain field, where it is further treated and dispersed into the soil.