Why is it crucial to ensure aircraft fittings are clean before attaching hydraulic servicing hoses?

Ensuring that aircraft fittings are clean before attaching hydraulic servicing hoses is critical because dirty fittings can introduce contaminants into the hydraulic system. These contaminants, such as dirt, debris, or moisture, can accumulate and lead to corrosion, blockages, or malfunction of vital components like valves and lines. Such damage can compromise the integrity and reliability of the entire hydraulic system, potentially leading to serious operational issues or failures during flight. By maintaining cleanliness, the risk of such contamination is significantly reduced, thus preserving the functionality and safety of the hydraulic system overall.