When performing an air test on a cast iron drain, waste and vent (DWV) piping at a pressure of 5 psi, the test gauge shall be marked at maximum _____ psi increments.

In plumbing, especially when dealing with pressure testing of drain, waste, and vent (DWV) systems, it's crucial to have precise measurements for assessing the integrity of the piping system. When conducting an air test on cast iron DWV piping at a pressure of 5 psi, it's specified that the test gauge needs to be marked at a maximum increment of 0.10 psi.

This level of precision is necessary because even slight variations in pressure can indicate leaks or weaknesses in the system. The smaller increment allows for more accurate monitoring of the pressure being applied during the test. If the increments were larger, such as 0.50 psi or more, then small leaks might not be detected, potentially leading to failure in the plumbing system over time.

Thus, the requirement for the gauge to be marked at maximum increments of 0.10 psi ensures that the testing is rigorous and effective, which is essential for maintaining the integrity of plumbing installations.