When required by the city, the owner of any property served by a building sewer carrying industrial wastes shall install a suitable control manhole in the building sewer to facilitate observation and sampling of wastes. Such manhole, when required, shall be accessible and safely located and shall be constructed in accordance with plans approved by the sewer department. The manhole shall be installed by the owner at his expense and shall be maintained by him so as to be safe and accessible at all times. (1976 Code § 11-3-5)