One to three closets - 4-inch XX cast-iron.
Four to eight closets - 5-inch XX cast-iron.
Eight to twelve closets - 6-inch XX cast-iron.

There are cases when 3-inch XX cast-iron pipe is used, but the practice is not recommended.

The soil pipe should be well supported and held in place. The connection between soil pipe and closet should be of lead to allow for any expansion of settling that might take place.

Material Of Soil Pipes

Soil pipe in common use today is made of light cast iron, tar-coated, extra heavy cast iron uncoated and coated, galvanized wrought-iron pipe, and steel pipe. The best kind to use depends upon the job and place where it is to be used. All kinds of bends and fittings can be had in any of the above-mentioned materials. In choosing the material of the pipe that is best to use, the following points should be carefully considered.

  1. First, new work or overhauling.
  2. Second, temporary or permanent job.
  3. Third, construction of building.
  4. Fourth, amount allowed for cost of materials on job.
  5. Fifth, size of job, that is, the number of toilets.
  6. Sixth, size of chases and pipe partitions.

Location Of Soil Pipe

The location of the soil pipe depends to a great extent upon the location of the toilets. The soil stack should be located on an inside partition. The horizontal pipe should not run over expensively decorated ceilings unless run inside of a trough made of copper or sheet lead. As far as possible, the pipes should be confined, to runs short, and the number of bends reduced.