_______ shall be required on all floor drains, in mechanical rooms or boiler rooms, and on open receptacles that receive the discharge from a temperature and pressure relief device discharge only.

The requirement for trap primers on all floor drains, in mechanical or boiler rooms, and on open receptacles that receive discharge from temperature and pressure relief devices stems from the need to maintain a proper water seal in traps. Trap primers are devices used to automatically supply water to a trap, ensuring that it remains filled with water. This is essential to prevent sewer gases from entering the building through the drainage system.

In the context of the specific locations mentioned in the question, the presence of temperature and pressure relief devices can cause intermittent discharges that may lead to evaporation of the water seal in traps if not adequately managed. By utilizing trap primers, the integrity of the trap is preserved, providing effective odor control and preventing the backflow of harmful gases, which is particularly important in mechanical and boiler rooms where the potential for hazardous conditions exists.

Other choices may refer to components of plumbing systems utilized for different purposes. Cleanouts are primarily for maintenance access to drainage systems, sump pumps are used for removing excess water from a location, and traps serve to hold water for blocking gases but do not inherently prevent evaporation without a primer system.