What is the primary requirement for indirect waste mains or branch mains?

Indirect waste mains or branch mains are specifically designed to handle waste that does not flow directly into the sanitary drainage system. One of the key characteristics of these systems is that they typically do not require a trap. This exemption is primarily because indirect waste is intended to discharge indirectly into a receptacle, such as a floor sink or a gravity-type sink, which is adequately designed to handle such waste without the need for trapping.

Since there is no direct connection to the sewer system, the potential for sewer gases leaking back into the space is significantly reduced, negating the need for a trap that would otherwise serve to prevent such occurrences. Therefore, the primary requirement is that these systems do not require a trap, simplifying installation and maintenance and allowing for more efficient drainage without the complications associated with traps, such as clogging or maintenance needs over time.

In contrast, the other choices involve conditions that are not applicable to indirect waste systems, either through being unnecessary or irrelevant to their design or operation.