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

The primary requirement for indirect waste mains or branch mains is that they do not require a trap. Indirect waste piping is used to transport waste from certain fixtures, such as sinks or floor drains, directly to the drainage system without any direct connection to the public sewer system. This design minimizes the risk of contaminants flowing back into the system and allows for proper drainage and venting.

Since indirect waste mains are intended to carry only liquid waste, the absence of a trap is allowed. Traps are generally installed to prevent sewer gases from entering the building and to retain water. However, in the case of indirect waste systems, the design and nature of how the waste is discharged—often at a higher elevation and through a regulated method—eliminate the need for a trap.

The other considerations listed, such as being trapped, vented, or limited to industrial zones, do not apply to the general requirements for indirect waste systems, as their design and function do not necessitate these additional features.