What must the pipe between the check valve and the outside hose coupling be equipped with?

The correct answer emphasizes the need for an automatic drain valve between the check valve and the outside hose coupling. This requirement is vital for preventing water from accumulating in the section of pipe and potentially causing freezing or other water damage. In climates where temperatures can drop significantly, stagnant water in this section could freeze and compromise the integrity of the fire service main.

An automatic drain valve ensures that any water trapped in the pipe is expelled safely, facilitating the maintenance of the system and preventing issues that could impair the fire service's functionality. This is particularly important in private fire service mains, where maintaining system reliability is crucial for effective fire protection.

Other potential options, while relevant in various contexts, do not specifically address this functionality. For example, a backflow preventer is used to protect the water supply from contamination but does not aid in draining the system. Similarly, a pressure gauge is essential for monitoring system pressure but does not directly relate to managing water within the pipe in this specific context. An approved sprinkler head is also not applicable here, as it does not address drainage needs. Thus, the automatic drain valve is specifically designed to address the concerns pertinent to the described location in the system.