What must be available at the job site according to manufacturer specifications?

The correct answer is that manufacturer's specifications must be available at the job site. This is essential because these specifications provide detailed instructions and requirements that need to be followed when installing plumbing systems. They typically include information on materials, installation techniques, and maintenance procedures specific to the products being used. Adhering to these specifications ensures not only that the installation meets the code and regulatory requirements but also that the performance and warranty of the products are upheld.

Having the manufacturer's specifications on-site allows contractors, plumbers, and technicians to reference crucial information as they work, ensuring they make the right decisions in the application and installation of the specified materials. This contributes to the overall safety, efficiency, and reliability of plumbing systems.