All materials used in the construction of sanitary sewers in the City shall be strictly first class and shall be in compliance with current specifications established under the Ohio Plumbing Code. No material shall be used in the work until it has been inspected and approved by the City Engineer. When required by the City Engineer, any or all materials entering into the construction of any work shall be tested by a reputable testing laboratory and any defective material or workmanship shall be at all times liable to rejection.