A septic tank is a device for treating feces and filtering out sediments. Its principle is that solid matter decomposes at the bottom of the tank, while the water-soluble substances rise to the top and flow out through pipes, preventing clogs. This allows sufficient time for the solid substances (such as feces and garbage) to hydrolyze. A septic tank refers to a small treatment structure that separates and sedimentates domestic wastewater and anaerobically digests sludge.

A septic tank is a fundamental facility for sludge treatment and also serves as a pre-treatment facility for domestic wastewater, its functions include:

1. Ensure the cleanliness of residential community environments, preventing the spread of domestic wastewater and pollutants.

2. Eliminate mosquito and fly larvae in the anaerobic digestion environment of septic tanks.

3. Temporary storage of sludge, anaerobic digestion of organic sludge, matured organic sludge can be used as agricultural fertilizer.

4. Pretreatment of domestic wastewater, sedimentation of impurities, and hydrolysis of large molecular organic matter into smaller organic molecules such as acids and alcohols, to improve subsequent wastewater treatment.