All sewer pipe shall be concrete, cast iron, vitrified clay, or other suitable material approved by the engineer. All jointing materials shall be of the bituminous type (asphaltic material with acid-resisting fillers), or lead. Bituminous compounds which are hot poured with a jute or oakum gasket are preferred. The hot poured compound shall be equal to or better than the Atlas mineral product “JC-60.” Ready-mixed bituminous compounds that may be packed cold into the joints is the alternate. These compounds shall be equal to or better than the Waterworks Supply Company “Plastiflex.” Names and addresses of suppliers will be furnished upon request.