What are the requirements for installing a backwater valve?

The requirement for installing a backwater valve emphasizes the importance of accessibility and proper placement relative to the building drain. A backwater valve must be accessible for maintenance to ensure that it can be easily serviced or cleared of debris when needed. This access is crucial for maintaining the functionality of the valve, as blockages can lead to backflow issues, potentially causing damage and health hazards.

Additionally, the valve is typically installed below the main building drain to effectively prevent sewage from backing up into the building during heavy rainfall or system overload. Positioning it in this manner allows the valve to function correctly, acting as a barrier to backflow while still permitting normal drainage from the building.

The other options do not align with the established requirements in plumbing codes, which stress both accessibility and correct placement of backwater valves. Thus, the correct choice focuses on ensuring proper installation that adheres to these critical standards.