California Code, Food and Agricultural Code (Formerly Agricultural Code) - FAC § 34621

Every restaurant, school, hospital, soda fountain, or other place where food or drink is served to the public, which sells milk, cream, ice cream, ice milk, buttermilk, or any combination of them for consumption on the premises, upon emptying any container of such a product, which container is to be returned to the milk distributor or manufacturer, shall rinse and drain the container, unless it is a glass container.