Which method must be provided to clean the system piping and hose reels after use?

The correct choice emphasizes the need for an integral method to blow out the system as part of the maintenance and cleanliness protocols for dry chemical extinguishing systems. During use, dry chemical agents can leave residues within the piping and hose reels that must be thoroughly removed to ensure the system operates effectively in the future.

Having an integral blowing-out method is particularly effective because it allows for the removal of these residues without the need for disassembling the system, which could introduce the risk of damaging components or compromising the system's integrity. This method not only promotes proper maintenance practices but also aligns with NFPA 17 standards, which focus on the operational reliability and longevity of extinguishing systems.

In contrast, while other options like flushing systems, manual cleaning procedures, or suction removal processes can be effective in certain circumstances, they may not provide the same level of efficiency or may require more extensive labor and time. Thus, an integral blowing-out method is preferred as it streamlines the cleaning process while ensuring thorough removal of dry chemicals from the system’s components.