Septic tanks are devices designed to treat and filter feces. The principle is that solid matter decomposes at the bottom of the tank, while the liquid matter rises to the top and flows through pipes, preventing clogs 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 anaerobically digests sludge.

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

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

2. Eradicate mosquito, fly, and worm eggs in the anaerobic digestion environment of septic tanks.

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

4. Preliminary treatment of domestic wastewater, sedimentation of impurities, and hydrolysis of large-molecule organic matter into smaller organic molecules like acids and alcohols, to improve subsequent wastewater treatment.