A septic tank is a device for treating feces and filtering out sediment. Its principle involves the decomposition of solids at the bottom of the tank, with the water-soluble matter rising to the top and flowing out through pipes, preventing clogs. This allows sufficient time for the solids (such as feces and garbage) to undergo hydrolysis. A septic tank refers to a small treatment structure that separates and sedimentates domestic wastewater and undergoes anaerobic digestion of sludge.

Septic tanks are fundamental facilities for sludge treatment and also serve as pre-treatment facilities for domestic wastewater, their functions are manifested in:

1. Ensure the environmental sanitation in residential communities, preventing the spread of domestic wastewater and pollutants in living environments.

2. Eliminate mosquito and fly 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. Pretreatment of domestic wastewater, sedimentation of impurities, and hydrolysis of large organic molecules into smaller ones like acids and alcohols, to enhance subsequent wastewater treatment.