What should be specified during the design phase to ensure optimal system functioning?

Specifying the maximum inlet pressure during the design phase is crucial for ensuring optimal functioning of an on-site sewage facility. The inlet pressure affects how sewage is delivered to the treatment system. If the pressure is too high, it can lead to issues such as overloading the system, causing backups or unpleasant odors due to inadequate treatment. Conversely, low pressure may prevent the proper movement of wastewater through the system. Therefore, establishing the appropriate maximum inlet pressure helps to maintain the system's efficiency and longevity, ensuring effective treatment and compliance with regulatory standards.

The other choices, while they may have implications for certain systems or conditions, do not directly influence the day-to-day operations and overall functionality of an OSSF as significantly as inlet pressure does.