When a subsoil drain system is connected by gravity to a storm sewer, it shall connect through a?

When a subsoil drain system is connected by gravity to a storm sewer, it is essential for the connection to prevent backflow into the system. A backwater valve serves this specific purpose by allowing the flow of water in one direction and preventing it from reversing. If the storm sewer level rises due to heavy rainfall or flooding, the backwater valve will close automatically, which protects the subsoil drain system from potential contamination and backflow issues.

In contrast, a cast iron gate valve is primarily used for isolation purposes rather than preventing backflow, and a check valve allows flow in one direction but may not be suitable or specifically required in every plumbing application, especially in the context of a subsurface drain that might need to be protected from backflow effectively. A 24 x 24 pit does not fulfill any of these flow-control requirements and is typically associated with different functions, such as providing access or storage, but it does not serve to prevent backflow. Therefore, the backwater valve is the most appropriate option for safeguarding the drainage system in this scenario.