Drainage and waste piping systems must be installed at what specified condition?

The correct choice involves the requirement for drainage and waste piping systems to be installed at a specified, constant grade. This is essential for ensuring that wastewater flows efficiently through the pipes without causing blockages or the potential for backflow. A constant grade allows gravity to effectively move the waste materials toward the drainage system.

In many plumbing codes and standards, including those from the NCCER, a minimum slope (often around 1/4 inch of fall per foot, depending on the pipe diameter) is specified to promote proper drainage. This consistent slope helps prevent stagnation of water and sewage, which can lead to odor problems, increased maintenance needs, and health hazards.

Other potential options, such as variable grades or random slopes, could lead to inconsistent flow and create areas where waste could accumulate, increasing the risk of clogs and system failures. Similarly, a focus solely on horizontal alignment does not address the need for gravitational flow, which is crucial for effective drainage and waste management systems.