Grease, oil and sand interceptors shall be provided when, in the opinion of the engineer or the city council, they 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 or dwelling units. All interceptors shall be of a type and capacity approved by the engineer and shall be located in such manner as to be readily and easily accessible for cleaning and inspection. These interceptors shall be constructed of impervious materials capable of withstanding abrupt and extreme changes in temperature, shall be of substantial construction, watertight, and equipped with easily removable covers which when bolted in place shall be gastight and watertight. All such interceptors shall be maintained by the owner, at his expense, in continuously efficient operation at all times.