What must installers have in their possession during the installation of an OSS?

During the installation of an Onsite Sewage System (OSS), it is essential for installers to have the approved design in their possession. The approved design outlines the specifications and requirements set forth by local authorities, ensuring that the installation adheres to regulations and guidelines. This document acts as a blueprint for the entire process, detailing the system's configuration, placement, and any special considerations that need to be taken into account to ensure proper functioning and compliance with health and safety standards.

Having the approved design is critical because it helps installers understand what materials to use, how the system should be constructed, and what local codes must be followed. This minimizes the risk of improper installation, which can lead to environmental contamination or system failure. Other options, while important in the broader context, do not provide the specific guidance necessary for the actual installation process as the approved design does. This ensures that the installer has a clear and accurate reference throughout the project.