All persons connecting to city service or laying their own private pipe shall be required to use only the pipe recognized and prescribed by the plumbing code, which has been adopted by the city of Aberdeen, up to and including two inches in size, and all the pipes shall be laid not less than eighteen (18) inches below the surface of the ground; except, that in ungraded streets, where the grade is already established, said services and pipes shall be laid at least eighteen (18) inches below said established grade. The superintendent will maintain private service from city mains in streets which are being graded or regraded and will have such access on private property as shall be necessary to maintain such pipes during the work, and shall as soon as practicable upon the completion of such work, relay said pipes in street. Owners shall maintain their private pipes from the end of the city service to and into their property. When necessary, the superintendent may slope service in on property to conform to the slope occasioned by the grading of the street and charge expense to the owner of the service. (Prior code § 10.18.090)