the length of the catering drainage main pipe should not exceed 21m. According to the relevant public information, too long drainage pipes are likely to cause problems such as pipe blockage and sewage backflow, which will affect the drainage effect and health and safety. Therefore, according to the requirements, the length of the catering drainage main pipe should not exceed 21 meters. The main restaurant drainage pipe refers to the drainage pipe connecting restaurants, canteens and other catering places, which is used to discharge the sewage and waste generated in kitchens and washing areas. It is usually made of PVC or other materials and has certain corrosion resistance and sealing performance. The catering drainage main pipe needs reasonable design, construction and maintenance to ensure that the discharged wastewater meets the national environmental protection standards and prevent the harm of sewage discharge to the environment and human beings. At the same time, restaurant managers should strictly abide by relevant laws, regulations and management systems, and strengthen the supervision and management of restaurant drainage.