A ________tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic treatment.

septic

The correct answer is Option (4)- septic

A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic treatment.

A septic tank is a key component of a septic system, which is a decentralized wastewater treatment system commonly used in rural or suburban areas where centralized sewage treatment facilities are not available. The septic tank receives and stores wastewater from homes and businesses. Inside the tank, solids settle to the bottom and form sludge, while lighter materials like grease and oils float to the top and form scum. The partially treated wastewater, known as effluent, flows out of the tank into a drain field or leach field, where further treatment occurs as it percolates through soil layers. Septic tanks provide basic treatment of wastewater by allowing solids to settle and decompose anaerobically, but additional treatment is necessary to fully purify the effluent before it returns to the environment.