A manhole is required when installing a rainwater leader on _______ inch or larger pipe.

When installing a rainwater leader, a manhole is required for a pipe that is 10 inches or larger in diameter. This requirement is based on plumbing codes and best practices, which dictate that larger pipes necessitate access points such as manholes for maintenance, inspection, and cleaning. Larger diameters can accumulate more debris and may require more frequent servicing. A manhole allows workers to easily access the system when needed.

Pipes of 8 inches and 6 inches do not typically require the same level of access and monitoring as those 10 inches and larger, as they can usually be managed through other access points or cleanouts that do not necessitate a full manhole. Thus, the requirement specifically focuses on the increased maintenance needs and challenges associated with larger pipes.