Which test requires the drainage system to be filled until water appears at the bottom of the lowest fixture?

The fixture flood test is designed specifically to assess the drainage system's integrity by filling it with water until it reaches the bottom of the lowest fixture, which is typically a sink or a toilet. This test helps to identify any leaks in the plumbing fixtures or the drainage system itself. By observing whether water appears at the bottom of the lowest fixture, it provides a clear indication of the system's performance under flood conditions.

This method simulates a condition that could occur during excessive rain or a plumbing issue, ensuring that the drainage system can handle such situations without leakage. The importance of this test lies in its ability to not only verify the watertightness of fixtures but also to ensure there are no flow restrictions or blockage in the system that could lead to backflow or other plumbing problems.