53 Pa. Stat. § 4624
The smallest diameter of any soil-pipe permitted to be used shall be three-inch. The size of soil pipes must be not less than those set forth in the following tables:
Maximum Number of Fixtures Connected to--
Size of Pipe. | Soil and Waste Combined. | Soil-Pipe Alone. | ||
Branch. | Main. | Branch. | Main. | |
3 In., | 7 fixtures, | 14 fixtures, | 3 water-closets, | 4 water-closets. |
4 In., | 48 fixtures, | 96 fixtures, | 8 water-closets, | 16 water-closets. |
5 In., | 96 fixtures, | 192 fixtures, | 16 water-closets, | 32 water-closets. |
6 In., | 268 fixtures, | 336 fixtures, | 34 water-closets, | 68 water-closets. |
If the building is six (6), and less than twelve (12), stories in height, the diameter shall be not less than five (5) inches; if more than twelve (12) stories, it shall be six (6) inches in diameter.
All soil-pipes must extend at least two feet above the highest window, and must not be reduced in size. Traps will not be permitted on main, vertical, soil or waste lines. Each house must have a separate line of soil and vent pipe. No soil, vent or waste line shall be constructed on the outside of a building. A two inch relief vent shall be required for first floor closets where a main vent stack of three inch or larger is in place, and fixtures are located above first floor.
Fixtures with--
One and one-quarter inch traps count as one fixture;
One and one-half inch traps count as one fixture;
Two-inch traps count as two fixtures;
Two and one-half inch traps count as three fixtures;
Three-inch traps (water-closets) count as four fixtures;
Four-inch traps count as five fixtures.
53 P.S. § 4624