What is the purpose of maintaining the high water level below the invert of the entering piping in an ejector basin?

Maintaining a high water level below the invert of the entering piping in an ejector basin primarily serves to prevent backflow and allow for air circulation. This configuration creates a hydraulic barrier that helps to mitigate the risk of sewage or wastewater backing up into the piping system. By keeping the water level elevated in the basin, the system can develop an effective seal against backflow while allowing air to circulate, which is essential for the proper operation of the ejector. The design thus ensures that any gases can dissipate and prevents the accumulation of harmful substances, contributing to a safer and more efficient drainage system.

While other options may provide beneficial aspects in their own right, they do not encapsulate the primary and critical function relating to the design of the ejector basin as effectively as the correct choice. This choice directly addresses the operational integrity and safety of the plumbing system involved.