53 Pa. Stat. § 4657
Water-closets when located in yard must be so arranged as to be conveniently and adequately flushed, and the water-supply pipes and traps protected from freezing by being placed in a hopper-pit at least four feet below the surface of the ground, the walls of which pit shall be constructed of hard burned brick or stone, laid in cement mortar, or of concrete. The walls for pit, where one (1) closet is installed, may be four (4) inches in thickness; or salt-glazed sewer-pipe, thirty-six (36) inches in diameter, may be used.
Where pit is for more than one (1) closet, the walls shall be nine (9) inches in thickness. The soil-pipe and traps used inside pit must be extra heavy cast-iron, and the trap to have hand-hold for cleanout purposes, with cleanout caulked in. If the closet is located in the rear of a soil- or vent-pipe, the drain on which it is located shall be vented with a four-inch pipe, carried above roof of closet, away from any opening or window. All outside closets shall be of the tank pattern. The water to be supplied to tank through an automatic seat-action valve. The waste from valve may be permitted to discharge on cement floor of pit, which shall be provided with four-inch trap and strainer. The enclosure of yard water-closets shall be ventilated by slatted openings; and there shall be a trap-door of sufficient size to permit of convenient access to the hopper-pit.
53 P.S. § 4657