Final answer:
An external sewer line inspection should be ordered before installing plumbing fixtures to detect issues early and ensure system integrity.
Step-by-step explanation:
An inspection for an external sewer line should typically be ordered before installing plumbing fixtures. Ordering an inspection at this stage allows for any issues to be identified and corrected before they are covered up by the building's interior structures or become more difficult and expensive to access and repair. While local authorities may have specific requirements, conducting an inspection before fixture installation is a good practice to ensure the integrity and proper function of the sewer system.