Wastewater-System Elements

The usual steps in planning a plumbing system are: (1) secure a sewer or wastedisposal plan of the site; (2) obtain architectural and structural plans and elevations of the building; (3) tabulate known and estimated occupancy data, including the number of persons, sex, work schedules, and pertinent details of any manufacturing process to be performed in the building; (4) obtain copies of the latest edition of the applicable codes, (5) design the system in accordance with code requirements, and (6) have the design approved by local authorities before construction is begun.
The typical plumbing layout in Fig. 14.9 shows the major elements necessary in most plumbing systems. Fixtures (lavatories, water closets, bathtubs, showers, etc.) are located as needed on each floor of the structure (Art. 14.7).
Each fixture is served by a soil stack, or waste stack, a vent or vent stack, and a trap (Fig. 14.9). Vertical soil or waste stacks conduct waste solids and liquids from one or more fixtures to a sloped house drain, or building drain, generally located below the lowest floor of the building. Each vent stack extends to a stack vent that projects above the building roof to a vent through roof (VTR). The vent stack may or may not have branch vents connected to it. Vents and vent stacks permit the entrance of fresh air to the plumbing system, diluting any gases present and balancing the air pressure in various branches. (See also Art. 14.20.)
Traps on each fixture provide a water seal, which prevents sewer gases from entering the working and living areas. In some areas, the plumbing regulations require installation of a building or house trap. The building drain delivers the discharge from the various stacks to the house trap, or building trap (Fig. 14.9),  which is generally provided with a separate vent. Between the building trap and public sewer, or other main sewer pipe, is the building sewer. The building sewer is outside the building structure, while the building trap is just inside or outside of the building foundation wall.

Where the building drain is below the level of the public sewer line, some arrangement for lifting the wastewater to the proper level must be provided. This can be done by allowing the building drain to empty into a suitably sized sump pit. The wastewater is discharged from the sump pit to the public sewer by a pneumatic ejector or motor-driven sewage ejector pump.
Pipe Supports. Pipes of wastewater-removal systems should be supported and braced in the same way as pipes of water-supply systems (Art. 14.8). Vertical pipes generally should be supported at every floor. Horizontal pipes should be supported at intervals not exceeding the following: cast-iron soil pipe, 5 ft and behind every hub; threaded pipe, 12 ft; copper tubing, 10 ft. Supports also should be provided at the bases of stacks.

Consideration should be given to the possibility of building settlement and its effects on vertical pipes and to thermal expansion and contraction of pipes, especially when the pipes have a high coefficient of expansion or are made of copper.
Clean-outs. A clean-out is an opening that provides access to a pipe, either directly or through a short branch, to permit cleaning of the pipe. The opening is kept plugged, until the plug has to be removed for cleaning of the sewer. In horizontal drainage lines, at least one clean-out is required for each 100 ft of pipe.
Clean-outs should be installed at the base of all stacks, at each change of direction in excess of 45, and at the point where the building sewer begins. For underground drainage lines, the clean-out must be extended to the floor or ground level to allow easier cleaning. Clean-outs should open in a direction opposite to that of the flow in the pipe, or at right angles to it.
In pipes up to 4 in, the clean-out should be the same size as the pipe itself. For pipes larger than 4 in, the clean-out should be at least 4 in in diameter but may be larger, if desired. When underground piping over 10 in in diameter is used, an access hole is required at each 90 bend and at intervals not exceeding 150 ft.