WAC 246-359-750
WAC 246-359-750. Water connector to factory assembled structures (FAS)
(1) A FAS with plumbing fixtures must be connected to the approved water service outlet by a flexible connector, such as copper tubing or other approved material, not less than three-fourths inch interior diameter.
(2) A separate water service shutoff valve installed on the supply side at or near the water service outlet for each FAS.