Final answer:
The rule in plumbing is that a trap arm smaller than 3 inches in diameter can change direction without a cleanout if the change does not exceed 135 degrees, not a specific measurement in inches. This allowance is designed to provide flexibility for installation without compromising maintenance access.
Step-by-step explanation:
The question relates to plumbing standards and regulations concerning the direction change of a trap arm. A trap arm, which is the pipe between a plumbing fixture and the p-trap, smaller than 3 inches in diameter may change direction without requiring a cleanout if the change in direction does not exceed 135 degrees.
This rule allows for a reasonable bending of the pipe to accommodate installation while still ensuring that cleanouts are provided when necessary for longer or more significant bends that could hinder the cleaning and maintenance process. There isn't a measurement in inches that restricts how far from the trap a cleanout needs to be if we're talking about changes in direction. Cleanouts are typically required based on the distance from the trap or the cumulative change in direction represented in degrees.