All soil and waste pipes must, whenever necessary, be securely fastened with wrought-iron hooks or straps.
Vertical soil and waste pipes must not be trapped at their base, as the trap would not serve any purpose, and would prevent a perfect flow of the contents.
Branch Soil and Waste Pipes.—The fixtures must be near the vertical soil and waste pipes in order that the branch waste and soil pipes should be as short as possible. The trap of the branch soil and waste pipes must not be far from the fixture, not more than two feet from it, otherwise the accumulated foul air and slime in the waste and soil branch will emit bad odors.
The minimum sizes for branch pipes should be as follows:
| Kitchen sinks | 2 inches |
| Bath tubs | 11/2 to 2 " |
| Laundry tubs | 11/2 to 2 " |
| Water-closets | not less than 4 " |
Branch soil and waste pipes must have a fall of at least one-quarter inch to one foot.
The branch waste and soil pipes and traps must be exposed, accessible, and provided with screw caps, etc., for inspection and cleaning purposes.
Each fixture should be separately trapped as close to the fixture as possible, as two traps on the same line of branch waste or soil pipes will cause the air between the traps to be closed in, forming a so-called "cushion," that will prevent the ready flow of contents.
"All traps must be well supported and rest true with respect to their water level."
Vent Pipes and Their Branches.—The purpose of vent pipes, we have seen, is to prevent siphoning of traps and to ventilate the air in the traps and pipes. The material of which vent pipes are made is cast iron.