All sewer-, soil-, and waste-pipes must be as direct as possible. Changes in direction must be made with "Y" or half "Y" branches, or one-eighth bends. Offsets in soil- or waste-pipes will not be permitted when they can be avoided; nor, in any case, unless suitable provision is made to prevent accumulation of rust or other obstruction. Offsets shall be made with forty-five degree bends, or similar fittings. The use of T-"Ys" (sanitary T's) will be permitted on upright lines only.
53 P.S. § 14814