A separate and independent building sewer shall be provided for every building and for every dwelling unit in buildings having more than one dwelling unit, except that multiple family buildings may perform a fixture count analysis to justify multiple dwelling connections on a single lateral. The analysis will be approved by the Director before the lateral is installed. 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, court, yard, or driveway, the building sewer from the front building may be extended to the rear building and 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 single connection.