A septic tank is a large, underground container made of concrete, fiberglass, or plastic that is used to treat and temporarily store wastewater from homes and businesses that are not connected to a municipal sewer system. It is a key component of a septic system, which is a decentralized sewage treatment system commonly used in rural and suburban areas.

The primary purpose of a septic tank is to separate and treat the solid and liquid components of wastewater before releasing the treated liquid, known as effluent, into the soil for further purification.

It's important to note that septic systems require regular maintenance, including periodic pumping to remove accumulated solids from the septic tank. 

Proper maintenance ensures the system's continued effectiveness and prevents problems like system failure or groundwater contamination. 

The frequency of pumping depends on factors like tank size, household size, and water usage patterns. Compliance with local regulations and guidelines for septic system maintenance is essential to protect both the environment and public health.