A separate and independent building sewer shall be provided for every building; except where one building stands at the rear of another on an interior lot and no private sewer is available or can be constructed to the rear building through an adjoining alley, courtyard or driveway, the building sewer from the front building may be extended to the rear building the whole considered as one building sewer, but the city does not and will not assume any obligation or responsibility for damage caused by or resulting from any such connection aforementioned. (Ord. 79-10, Art. IV § 4)