Septic tank is a kind of equipment to treat feces and filter and precipitate them. The principle is that the solidified object decomposes at the bottom of the pool, and the hydrated object on the upper layer flows away into the pipeline, which prevents the pipeline from blocking and gives the solidified object (feces and other garbage) sufficient time to hydrolyze. Septic tank refers to a small treatment structure that settles domestic sewage and anaerobic digests sludge.

Septic tank is not only a basic sludge treatment facility, but also a pretreatment facility for domestic sewage. Its functions are as follows:

1. Ensure the environmental sanitation of the living community and avoid the diffusion of domestic sewage and pollutants in the living environment.

2. Kill mosquito and fly eggs in the anaerobic septic working environment.

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

4. Pretreatment of domestic sewage (primary treatment), precipitation of impurities, and hydrolysis of macromolecular organics into small molecular organics such as acids and alcohols to improve subsequent sewage treatment.