In gravelless systems, the pipe must be marked to indicate what?

In gravelless systems, marking the top of the pipe is essential for several reasons. This marking helps to ensure proper installation and maintenance of the system. When maintenance personnel or inspectors know the location of the top of the pipe, they can more easily access it for repairs, inspections, or cleaning without having to excavate unnecessarily.

Additionally, understanding the position of the pipe relative to the surface plays a vital role in ensuring that the system functions as intended, especially regarding the flow of wastewater and prevention of blockages. Proper marking also aids in complying with local regulations that may require such practices to safeguard the integrity and function of the septic system.

The other options would not provide the critical information necessary for the effective management and maintenance of the system. Depth, length, and diameter markings do not offer the immediate surface orientation needed for quick and efficient service, which is why knowing the top of the pipe is the most important.