P-904.5 Minimum Size of Soil and Waste Pipe

No soil or waste stack shall be smaller than the largest branch draining into it regardless of the height of the building. Soil stacks receiving the discharge of water closets shall not be less than 3 inches in diameter, as provided in Table P-904.4. Three-inch Soil stacks shall be limited to two water closets. No horizontal soil pipe or waste pipe draining pedestal urinals or water closets shall be less than 3 inches in diameter. When using 3-inch ideal bends (closet bends) to receive the discharge of water closets, this fitting shall be a blind bend containing no drainage connections for other fixtures. No waste pipe shall be less than 1-1/4 inches in diameter except that waste pipe drip lines from soda fountains, coffee urns and refrigerator cases shall be minimum 1-inch nominal diameter and not over 12 feet in length when trapped and discharged into an open fixture. Fixture branch pipes shall conform to Section P-506.

The minimum size of the main house drain receiving the discharge of water closets shall be 4 inches inside nominal diameter.