53 Pa. Stat. § 14823
Where rows of fixtures are placed in a line, fittings of not less than forty-five (45) degrees to the horizontal must be used on vent lines to prevent filling with rust or condensations; except on brick or tile walls, where it is necessary to channel same for pipes, ninety (90) degree fittings will be allowed. Trapped vent-pipes are strictly prohibited. No vent-pipe from house side of any trap shall connect with ventilation pipe, or with sewer-, soil-, or waste-pipe. Vent-pipes from several traps may be connected together, or may be carried into the main vent line above the highest fixture. Where one vertical vent line connects with another, a "Y" fitting must to used. Branch vent-pipes must be connected as near to crown of the trap as possible.
53 P.S. § 14823