A septic tank is a device for treating feces and filtering out sediment. Its principle is that solid matter decomposes at the bottom of the tank, while the liquid hydrolyzed matter enters the pipeline and flows away, preventing pipeline blockages and allowing sufficient time for the solid matter (faeces and other waste) to hydrolyze. A septic tank refers to a small treatment structure that separates and sedimentates domestic wastewater and undergoes anaerobic digestion of sludge.

A septic tank is a basic sludge treatment facility and also a pretreatment facility for domestic wastewater, its function is manifested in:

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

2. Eliminate mosquito, fly, and worm eggs 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. Preliminary treatment of domestic wastewater, sedimentation of impurities, and hydrolysis of large organic molecules into smaller organic molecules such as acids and alcohols, to improve subsequent wastewater treatment.