A septic tank is a device for treating feces and filtering out sediments. Its principle involves the decomposition of solids at the bottom of the tank, with the water-soluble substances rising to the top and flowing through pipes, preventing blockages. This allows sufficient time for the solids (such as feces and waste) to undergo hydrolysis. 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 fundamental sludge treatment facility and also a pre-treatment facility for domestic wastewater, its functions are manifested in:

1. Ensure the environmental hygiene in residential communities, 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. Pretreatment of domestic wastewater, sedimentation of impurities, and hydrolysis of large organic molecules into smaller ones such as acids and alcohols, to improve subsequent wastewater treatment.