What should the distance from the end of a waste pipe above the rim be based on?

The correct answer is based on the principle of preventing backflow and ensuring proper drainage in waste systems. The distance from the end of a waste pipe above the rim of the receptacle (such as a sink or toilet) should be two times the diameter of the waste pipe. This guideline helps maintain an effective air gap, which is crucial for preventing contamination and the siphoning of wastewater back into the clean water supply.

By having the end of the waste pipe positioned at this specified distance, it minimizes the risk of splashing and creates a buffer that allows for the free movement of air, thus preventing negative pressure conditions that could lead to backflow. A distance of two times the diameter is deemed sufficient for effective drainage while safeguarding public health by reducing the chances of cross-contamination.

Other options suggest lesser or greater distances, which could compromise the drainage functionality or safety of the plumbing system. For example, if the distance were equal to or less than the pipe diameter, it may not provide adequate protection against backflow and could allow splashes that introduce contaminants into the potable water supply. Conversely, a distance greater than two times the diameter may not enhance safety in practical terms and could lead to unnecessary complications in plumbing design.