The size does not increase with the number of fixtures. Very few of a hundred closets in a building would ordinarily be flushed simultaneously. A 5-inch stack would answer well for 100 closets in a tall building where the toilet-rooms are superimposed, as shown in Fig. 161, which outlines the soil, waste, and vent pipes of several groups of fixtures, rain-water leaders, etc. If the same number of closets were at one elevation, and the fall only moderate, common sense would dictate a 6, 8, or 10-inch line, with 4-inch fixture branches. The velocity with which the water will flow away should be a prime factor, but sizes in soil and waste pipes are far more a matter of empiricism than in supply work. A soil pipe not too large is scouring in a sense. This point is erroneously argued in favor of small waste pipes. If a soil pipe too small for the duty should be installed, ordinary usage would develop the fact quickly. But in a waste outlet, where grease is likely to accompany the water, a pipe large enough to carry the waste easily when the pipe is new, may be-. come choked after a considerable period of time, and merely because it is of the size so-called "self-scouring." A house line which may be much too large for the waste will be likely to choke from floating matter adhering to the sides above the water line until overhanging ridges are formed that break down in the channel. Being too heavy for the water to push along, this matter acts as a dam, and complete stoppage soon results. This is why large sewers are built with elliptical bottom section. Having variable flows to take care of, the depth of water produced by ordinary usage cleanses the conduit, and keeps it in much better condition than if round conduits of the same capacity were employed.
Slope. With due respect for appearance, all the fall possible should be given lateral soil and waste lines. About . % inch to the foot (one degree) is taken as the minimum. With cast pipe and leaded joints, much more than this can be given, by gaining change of direc tion in setting the joints. With screwed fittings for wrought pipe, tap ped, pitched one degree from the nominal angle, less latitude to vary the fall is offered. Considerable variation is possible, however, by cutting pitched threads on the pipe. In positions where the cutting of one pitched thread entails the work of cutting another with the pitch just opposite that of the first in order to follow the perpendicular again, the work is irksome and is seldom resorted to. Cast fittings, threaded, for drainage work, are recessed in the ends, so that, when screwed on the pipe, the pipe and interior of the fitting are of the same diameter, thus presenting no jog or broken edges to favor stoppage. Stoppage of drains of any kind is likely from many causes; and during installation, trap-screw ferrules, or tees with brass plugs, according to the kind of pipe being used, should be provided along the line, as shown in Fig. 162, so as to make the work of cleansing as convenient
and inexpensive as possible.
Sizes of Soil and Waste Pipe. The usual sizes for soil and waste work are: 5-inch for ordinary house main (horizon tal); 4-inch for 1 to 4 closets; 5-inch horizontal branch from 5-inch stack for a battery of five or more closets; 5-inch stack for any ordinary number of fixtures; main vent stack, same size as soil-stack; loop vent, same size as stack; crown-vent stacks, 2 or 3-inch; slop-sink stacks, 3 or 4-inch; closet connection, 4-inch; closet crown vent, 2-inch; slop-sink con nection, 3-inch; slop-sink vent, 2-inch; urinal stacks, 3-inch; uri nal branch wastes, 2-inch; urinal trap vents, 14 to 2-inch; bath stacks, 3-inch; bath-waste connection, 2-inch; lavatory wastes, 2-inch. The 2-inch refers to the size of cast pipe used in the case of lavatories and baths; the lead trap and connections of these, and often of other fixtures, are made 1f-inch. Small lavatories often have 11-inch waste. The crown vent is usually one size less than the trap for all but closets and slop sinks. Of late, bath-waste outlets are fre quently made 2-inch. Kitchen-sink stacks are made 3-inch; single sinks or branch waste for one sink or set of trays, 2-inch, with 2-inch trap and 14-inch crown vent.
Local Ventilation. A local vent is a pipe leading air from the bowl of a closet or through the outlet of a urinal to carry away odors with a current of air fed by the air of the room. In Fig. 163 are shown two openings for urinals where the roughing-in pro vides for local ventilation for the urinal bowls in a way that is equivalent to the local vent pipe to a closet bowl. V is a general vent stack, and W the urinal waste stack. Instead of putting in crown vents for the traps, the branch waste becomes a vent at the junction of the trap branches, and loops back into the general vent stack. There is sufficient ventilation in this case for two reasons—the traps are close to the line; and the current up the main local vent stack is induced and maintained by a fan motor, which, in drawing the odors from the urinal bowl, creates more or less suction on the house side of the trap seals and counteracts the tendency toward siphonage on the sewer side. The roughing-in shown, is hid by marble slabs in the finished work.
A section of the marble back, with urinal and vent and waste connection, is shown in Fig. 164, which makes clear what is meant by local urinal ventilation. The difference between it and local closet ventilation, is that as the trap for the urinal is not in the urinal proper, the current from the room passes through the urinal outlet except while it is flushing; while in the closet the ,local vent connection is made to the bowl above the visible water-level, because the trap below interferes connecting it other wise.