Each cleanout shall be installed so that it opens in what direction relative to the flow of soil or waste?

The correct answer is that each cleanout shall be installed so that it opens opposite to the flow of soil or waste. This design is fundamental for effective maintenance and accessibility. By having the cleanout opening in the opposite direction of the flow, it allows for easier access when cleaning or clearing blockages within the plumbing system.

This positioning enables the technician to insert cleaning tools or equipment without having to navigate against the flow, which could complicate the removal of obstructions or maintenance procedures. Additionally, it helps to minimize the release of any waste materials during the cleaning process, contributing to a more sanitary working environment.

In contrast, if a cleanout were to open in the same direction as the flow, it could lead to difficulties in accessing and addressing potential clogs, making maintenance more challenging. This could also pose a risk of spillage or backflow, which is undesirable in plumbing systems. Other orientations, such as diagonal or in any direction, do not provide the same level of functionality and convenience as having the cleanout facing opposite to the flow.