Which of the following methods is NOT included in sewer testing methods?

The correct answer is that sewage is not considered a method for sewer testing. In sewer testing, different methods are utilized to evaluate the integrity and performance of sewer systems.

Air testing involves introducing air into the sewer piping system to check for leaks, ensuring that all connections and pipes are airtight and can handle the expected pressure. Water testing, on the other hand, uses water to fill the sewer lines to detect any possible leaks or weaknesses in the system; it's a straightforward method that can also provide insights into flow characteristics.

Mandrill testing refers to a method using a device that can inspect and analyze the interior condition of the sewers, providing a detailed look at the pipes without needing to physically access them.

Sewage itself does not represent a method for testing; rather, it is the substance that the sewer system is designed to transport. In the context of sewer testing, it's crucial to distinguish the types of methods aimed at assessing system performance from the materials or waste that the system handles.