What does a stop box do in plumbing?

A stop box in plumbing is primarily designed to allow access to underground valves or water shut-off points without having to dig up the ground. It enables maintenance personnel to easily operate the valve for repairs or emergencies. While controlling water flow and providing support are essential functions within plumbing, a stop box specifically facilitates accessibility to the pipe systems rather than directly managing flow or stability.

The other options might relate to different plumbing components; for instance, controlling water flow typically pertains to valves, while providing a liquid seal against sewer gases is the role of traps. Supporting pipes is essential for structural integrity, but it does not apply to the function of a stop box. Thus, the primary purpose of a stop box aligns with allowing pipe access, making this the correct understanding of its role in plumbing systems.