Massachusetts Plumbers Journeyman Practice Exam

Where are slip joints or couplings allowed to be used?

1. Only at the trap inlet

2. Anywhere downstream of the trap

3. Within the trap seal if a metal-to-metal ground joint is used

4. Only on vertical runs

The correct answer is: Within the trap seal if a metal-to-metal ground joint is used

Slip joints or couplings are specifically allowed within the trap seal when a metal-to-metal ground joint is used due to their ability to provide a reliable seal while allowing for disconnection during maintenance or servicing. These joints are beneficial in plumbing systems since they can accommodate slight misalignments and movements of connected pipes. Importantly, the use of a metal-to-metal connection enhances the integrity of the seal and prevents leaks, particularly in critical areas like the trap seal that are essential for preventing sewer gases from entering a living space. In other contexts, while different applications of slip joints may be permissible, they are not necessarily suitable for all areas within a plumbing system due to potential concerns related to leakage and structural integrity. For instance, the regulations may discourage their use in areas that experience significant pressure or movement, emphasizing the importance of strong and secure fittings in those locations.