The drainage ventilation system has various types, such as top extension ventilation tube, main ventilation tube, auxiliary ventilation tube, combined ventilation tube, ring ventilation tube, appliance ventilation tube, confluent ventilation tube and special ventilation tube, which are used in different positions. Among them, hood ventilation tube is suitable for the installation of water storage tanks and water tanks. A duct connected with the atmosphere for the purpose of air circulation, stable pressure, and failure of waterproof seal in a drainage system.