Massachusetts Plumbers Journeyman Practice Exam 2025 - Free Plumber Journeyman Practice Questions and Study Guide

The correct height for a standpipe serving a clothes washing machine is 30 inches above the base of the machine. This height requirement is established to ensure that the standpipe effectively prevents siphoning, which can lead to improper drainage or backflow of wastewater into the washing machine. A standpipe that is too short may allow water to flow back into the appliance, creating potential health hazards, creating messes, or causing damage to the machine itself.

The standard height of 30 inches also helps accommodate the washing machine's discharge hose, ensuring proper drainage without the risk of overflowing. The design of the plumbing system should always adhere to these standards to maintain efficient and safe operation.

While there are other height measurements provided, none serve the dual purpose of preventing siphoning and ensuring proper function of the washing machine as effectively as the 30-inch requirement.