Sanitary drainage pipe that is less than _____ in diameter requires that the cleanouts be the same size as the drainage pipe they serve.

In plumbing systems, the requirement for cleanouts is crucial for maintenance and accessibility. When it comes to sanitary drainage pipes, the rule is that the diameter of cleanouts should match the diameter of the drainage pipe they serve if the diameter is less than 4 inches. This ensures that the cleanout can adequately accommodate any blockages or issues that may arise within the drainage system, allowing for efficient cleaning and maintenance.

Using a cleanout that is the same size as the drainage pipe enhances the effectiveness of the cleaning process, as it provides a direct path through which blockages can be removed. This is especially important in smaller diameter pipes, where a smaller cleanout might impede access and make it harder to resolve issues. Therefore, for any sanitary drainage pipe with a diameter less than 4 inches, maintaining the same size for the cleanouts is essential for proper function and convenience.