What is the standard length of a horizontal run of 1 ½ inch drain pipe without a cleanout required?

The standard length of a horizontal run of 1 ½ inch drain pipe without requiring a cleanout is indeed 40 feet. This standard is established in various plumbing codes, which dictate the maximum distance for a horizontal drain run before a cleanout is necessary. The purpose of this requirement is to ensure accessibility for maintenance and cleaning of the drain system.

In practice, if the length of the drain extends beyond this specified distance, it may become more difficult to clear clogs or perform necessary inspections, which can lead to issues in the plumbing system. Therefore, adhering to the 40-foot standard helps maintain proper function and access within a plumbing installation.