According to code, the minimum size of a clean out plug on a 4 inch soil or sewer drain must be ______ inches?

The correct answer identifies that the minimum size of a cleanout plug on a 4-inch soil or sewer drain must be 4 inches. This requirement is primarily based on plumbing codes, which stipulate that cleanout fittings must be appropriately sized to facilitate effective access for cleaning and maintenance of the drainage system. A 4-inch cleanout plug allows for the insertion of adequate tools and ensures that blockages can be addressed efficiently.

Having a properly sized cleanout is crucial for the overall functionality of the drainage system. It enables plumbing professionals to clear debris, inspect the interior condition of the pipe, and perform necessary maintenance without having to disrupt the plumbing layout excessively. In contrast, options that suggest smaller cleanout sizes would not provide sufficient access for regular maintenance and could potentially lead to complications in maintaining the drainage system.