The end of a waste pipe should terminate at least ____ above the rim of a sink or receptacle directly connected to the drainage system.

The correct answer of 2 inches is based on guidelines set forth in plumbing codes to prevent backflow and contamination of the water supply. When a waste pipe, such as that from a sink, discharges directly into a receptacle, it is critical to maintain a certain height above the rim to ensure that wastewater does not siphon back into the clean water source.

The 2-inch minimum height creates a physical barrier that helps prevent the potential for cross-contamination should there be negative pressure in the drainage system. This scenario can happen due to various factors, including sudden changes in flow or blockages downstream, which can create a vacuum effect.

By adhering to this 2-inch requirement, effective drainage and sanitation standards are upheld, thus significantly reducing the risk of health hazards associated with contaminated water entering the potable supply. This standard is a key aspect of maintaining public health and safety within plumbing systems.