The vent-pipe system is also an additional means of ventilating the plumbing system of the house, already partly ventilated by the extension of the vertical pipes above the roof and by the fresh-air inlet. The principal objection urged against the installation of the vent-pipe system is the added expense, which is considerable; and plumbers have sought therefore to substitute for the vent pipes various mechanical traps, also nonsiphoning traps. The vent pipes are, however, worth the additional expense, as they are certainly the best means to prevent siphonage and back pressure, and are free from the objections against the cumbersome mechanical traps and the filthy nonsiphoning traps.
CHAPTER VII
Plumbing Pipes
The House Drain.—All waste and soil matter in the house is carried from the receptacles into the waste and soil pipes, and from these into the house drain, the main pipe of the house, which carries all waste and soil into the street sewer. The house drain extends from the junction of the soil and waste pipes of the house through the house to outside of the foundations two to five feet, whence it is called "house sewer." The house drain is a very important part of the house-plumbing system, and great care must be taken to make its construction perfect.
Material.—The material of which house drains are manufactured is extra heavy cast iron. Lighter pipes should never be used, and the use of vitrified pipes for this purpose should not be allowed.
Size.—The size of the house drain must be proportional to the work to be performed. Too large a pipe will not be self-cleansing, and the bottom of it will fill with sediment and slime. Were it not for the need of carrying off large volumes of storm water, the house drain could be a great deal smaller than it usually is. A three-inch pipe is sufficient for a small house, though a four-inch pipe is made obligatory in most cities. In New York City no house drains are allowed of smaller diameter than six inches.
Fig. 22.
SYSTEM OF HOUSE DRAINAGE, SHOWING THE PLUMBING OF A HOUSE. (H. Bramley.)