what size drain pipe should be used for a toilet
The stack itself should be at least 4-inches in diameter. A T will be required to hook the drain pipe itself into the stack. The toilet drain pipes should be 3 or 4 inches in diameter and slope down toward the stack at a rate of 1/8 to 1/4 inch per foot of length or should be vertical to the ground. From trap to vent on a toilet with a 3-inch pipe should be no longer than six feet, and for a 4-inch pipe the distance is ten feet.