Every building shall be separately and independently connected with a public or private sewer when there is such in the street abutting on the lot occupied by such building.

    The entire plumbing and drainage system of every building shall be entirely separate and independent from that of any other building, except where there are two buildings on one lot, one in the rear of the other; then if there is no sewer in the alley to which the rear building can be connected, the sewer in front of the building may be extended to serve the rear building. (Prior code § 29-1-7)