Grease, oil and sand interceptors shall be provided, when, in the opinion of the city, such are necessary for the proper handling of liquid wastes containing grease in excessive amounts or any flammable wastes, sand and other harmful ingredients; except, that such interceptors shall not be required for private living quarters. All interceptors shall be of a type and capacity approved by the city and shall be located so as to be readily and easily accessible for cleaning and inspection, and shall be maintained by the owner, at his expense, in continuously efficient operation at all times.