Under what condition must indirect waste pipes be trapped?

Indirect waste pipes must be trapped when they are used in certain conditions to prevent the potential backflow of sewage gases and maintain the integrity of the plumbing system. The requirement for trapping is specifically tied to the configurations and lengths of the piping.

When the length of the horizontal piping exceeds a certain threshold, in this case, 30 inches, trapping is necessary to ensure that wastewater flows properly and prevent siphoning. Additionally, if the total piping throughout the system exceeds a specified measurement, in this scenario, 54 inches, trapping is also mandated.

The reasons for these conditions are based on the need for effective drainage and venting within plumbing systems. If indirect waste pipes do not have traps installed under these situations, they could allow odors and gases to enter the living spaces, creating health hazards. Proper trapping aids in keeping the system functioning and safe.

Thus, the correct answer is both scenarios must be taken into account to ensure compliance with plumbing codes and to protect public health and safety.