How to Determine a Toilet Slope
- 1). Measure the distance in feet from the toilet to the soil stack line.
- 2). Multiply the number of feet in distance by 1/4 inch per foot to find the number of inches the pipe should drop over the run. For instance, if the soil stack line is 4 feet from the toilet, the pipe should drop 1 inch because 4 feet x 1/4 inch per foot = 1 inch.
- 3). Mark the spot on the soil stack directly across from the opening of the toilet drain.
- 4). Measure down the soil stack the number of inches of calculated drop for the pipe. This is where the 3-inch-diameter toilet drain line will meet the soil stack for drainage to the main drain and out to the sewer.
Source...