Which fitting is used for the trap arm of a lavatory?

The tailpiece is specifically designed for use in the trap arm of a lavatory. It connects the sink drain to the trap, forming part of the drainage system that prevents sewer gases from entering the living space. The tailpiece is typically a short pipe that extends directly from the lavatory's drain outlet and serves as a conduit for water and waste to flow into the trap.

In the context of plumbing fittings, the function of the tailpiece is integral as it is sized and shaped to fit the existing plumbing fixtures, ensuring a tight and watertight connection. Its ability to align correctly with the trap and other plumbing components solidifies its importance in the proper installation of lavatory drainage systems.

Other options such as cut pipe, short nipple, and coupling serve different purposes within plumbing systems. Cut pipe may refer to any section of pipe that has been cut to length and doesn’t imply a specific function, while short nipple is typically a short piece of pipe used to connect two fittings. Couplings serve to connect two sections of pipe, but they do not have the specific role of transitioning from a lavatory drain to a trap. Thus, the tailpiece is the fitting that is purposefully designed and used for this function.