Massachusetts Plumbers Journeyman Practice Exam 2026 - Free Plumber Journeyman Practice Questions and Study Guide

The correct diameter for connecting domestic food-waste grinder units is 1½ inches. This size is recommended to ensure adequate drainage and prevent blockages within the plumbing system. Food-waste grinders typically discharge a mixture of water and solid waste, which can require a sufficient diameter to allow for smooth flow and reduce the risk of clogs.

Larger drain diameters, such as 2 inches or 3 inches, although capable of handling more significant volumes, are not necessary for the typical output of a domestic food waste disposal unit. If the drain were smaller than 1½ inches, it could lead to problems such as slow drainage or backups in the system, especially when the disposal is used frequently. The 1½ inch diameter strikes a balance, providing enough capacity while adhering to standard plumbing practices for residential installations.