Which of the following describes an example of a prohibited trap?

A full "S" trap is an example of a prohibited trap due to its design, which makes it highly susceptible to trapping air pockets or siphoning. In plumbing systems, traps are necessary for preventing sewer gases from entering buildings while allowing wastewater to pass through. However, each type of trap is designed to maintain a specific water seal to achieve this goal.

Full "S" traps create a configuration that can lead to the water seal being compromised. When wastewater flows through the "S" shape, it can cause a pressure differential that may siphon out the water, effectively removing the barrier intended to block sewer gases. This makes these traps ineffective and presents a health hazard. Consequently, they are banned in modern plumbing codes.

By understanding the design flaws associated with full “S” traps, plumbers can make informed decisions about trap selection that ensure both safety and compliance with current plumbing standards.