House Drains.—Whether the house drain should be of cast iron or earthen ware is an open question. It is preferable to have a cast-iron drain carried with a good fall (one in sixty) along the side-wall, rather than to have an underground tile pipe which is liable to crack or he damaged by roots of trees, rats, etc. In good practice only iron pipe is permitted within doors and tile pipe outside the building. The iron pipe should be carried three feet outside the foundation walls in order to avoid any risk of breakage frOm the building settling.
The Laying of Drains. —The laying of underground drains is usually entrusted to unskilled labourers ; vet it should be carefully done under competent supervision. Iron pipe is preferable indoors. If tile pipe is chosen for economy's sake, a ditch should be dug two feet wide, so as to give ample room for action ; the bottom should he beaten hard, and have a slope of one foot in sixty, with a slot to receive each huh. The cement should fill the entire circle of the hub, and, after laying each length of pipe, the interior should be scraped clean with a piece of cane having a swab at one end to remove all obstructions, Soil-Pipes.—The first soil-pipes were of lead, and hand-made. They are stilt used in Great Britain, but in the United States they have been replaced by iron, owing to the risk of sagging, corrosion, driving nails, and gnawing rats. About 1867 it was found that the lead at the crown of water-closet traps corroded and allowed sewer-gas to escape. The soil-pipes at first reached only as far as the bathroom or second floor ; but,upon this discovery being made, they were extended to the roof, at first of small size, later of full size, and finally they were enlarged to five and six inches, and the end divested of cowls and " return-bends," which tend to close the pipe by the freezing of the condensed moisture.
Ventilation of Drains.—Even if house-drains are of good material and properly connected, there is still risk of the traps or fixtures losing their seal by evaporation or siphonage, so as to permit the entrance of sewer-gas into living-rooms. A thorough circulation of air is therefore necessary throughout the entire drainage system, so that, in case of a leak or accident, only diluted foul air can escape. To secure such ventilation a running trap is placed upon the main drain between the house and the sewer or cesspool.
with a fresh-air inlet from just inside the trap extended to the ground-level and ending in an open box covered by an iron grating, which should be kept free from dirt. The air, entering at this opening, circulate through the whole drainage, and pass out at the roof so as to ventilate every pipe and drain (see Fig. 352).
Water-Traps.—Water-traps have been used for many years in chemists' laboratories to prevent the passage of gases, and they are thoroughly reliable. They depend for security upon a water-seal, perhaps only an inch or two in depth. Since this will soon evaporate in warm weather or freeze in winter, the supply must be replenished at intervals. Therefore, any plumbing fixture which is not in constant use should be cut off. Siphonage is due to the pulling action of one trap upon another, or of a column of water emptied into a soil or waste pipe and passing by a branch trap on a lower floor. In either case the water-seal in the second trap is forced, or the trap partly emptied and its efficiency destroyed. This action can be prevented by attaching a back-air " pipe to the crown of the trap. and carrying the same above the roof. For an explanation of siphonage, see Figs. 353, 354.
Valve traps are not sanitary, except to resist tidal pressure. Most " bottle " or pot traps are miniature cesspools, which collect grease and filth ; patented devices are usually makeshifts, and are not permitted by boards of health in large cities. The " Sanoz " trap is an exception to the rule, and has been officially approved and used in public buildings (sec Figs. 355-359).
Water-Closets.—The best plumbing fixtures are cheapest in the long run. The siphon-jet water-closet is absolutely self-cleansing, but it consumes a great deal of water. The low cistern is almost noiseless, which is advantageous in many situations. The closet requires attention to keep it sweet and clean. The long hopper soon gets foul and is out of date ; whereas a short-hopper, with an enamelled iron trap, costs little, and is economical and sanitary ; it is especially adapted to servants' use. When houses are not occupied during the winter, the water-closet traps should be sponged out and filled with kerosene or glycerine to prevent freezing.