What must be done to underground mains before connecting to an NFPA 13 R system?

Flushing underground mains until clear is a critical step before connecting to an NFPA 13 R system. This procedure ensures that any debris, dirt, or contaminants that may have accumulated in the piping system are removed. Such contaminants can impede the flow of water and may affect the proper functioning of the fire protection system. NFPA 13 R systems, which are designed for residential fire protection, rely on clear and unobstructed water supply to ensure effective performance in case of a fire. Properly flushing the mains helps to maintain the integrity of the system and ensures compliance with safety standards, preventing potential hazards associated with blocked or contaminated lines.