Septic tanks are devices used for treating feces and filtering out sediment. The principle involves the decomposition of solid matter at the bottom of the tank, with the water-soluble substances rising to the top and flowing out through pipes, preventing blockages. This allows the solid matter (feces and other waste) sufficient time to undergo hydrolysis. A septic tank refers to a small treatment structure that separates and settles 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, with their functions manifested in:

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

2. Eradicate 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. Pretreat domestic wastewater by sedimenting impurities and hydrolyzing macromolecular organic matter into smaller molecules such as acids and alcohols, thus improving the subsequent wastewater treatment.