Fig. 14.

Fig. 15.

Where the ground about the house is so nearly level that the fall requisite for a proper subsoil irrigation system cannot be obtained, some relief from the annoyance of an overflowing cesspool may be secured by laying lines of open-jointed sole tile directly out from the cesspool, radiating, if necessary, in all directions, for the purpose of increasing as much as possible the surface of absorbent soil reached by the sewage. The pipes should be laid as near the surface as practicable, without allowing the sewage to back up into the cellar, so as to bring the liquid which overflows through them into the porous and oxidizing upper soil, which will take up and destroy a large amount of sewage in this way before the pipes become clogged. After this has occurred, it is a trifling matter to take them up and clean them out; and, if the ground around them has become saturated, they may be relaid in fresh soil. Even where the house is connected with a sewer, or where the cesspool, or other system of disposal, is in good order, sewage will often back up and overflow the basement through the choking of a main trap with grease. The main trap is simply a dip in the line of the main drain, intended to keep air from the sewer or cesspool out of the house pipes, and usually has a hand-hole for cleaning (Fig. 16), closed with a plug or brass screw, and a « foot vent," or inlet-pipe, on the house side of the trap, open to the air, for admitting air to the system of house pipes. Such main traps are sometimes found inside the house, and sometimes in pits outside, the practice varying with the locality, and with the period at which the house was built. Whatever the style of trap, or the period to which it belongs, it is sure to give trouble sooner or later; and the householder who does not wish to see his basement water-closet occasionally overflowing, or the laundry wash-trays filled with foul water, must take care to have the trap cleaned out at regular intervals. It is still better, in building a new house, to leave the main trap out altogether; or, if it is found in a house already built, to have it removed. Unfortunately, however, the proprietor must consult the local Board of Health before he ventures to do anything about the matter, for there is no question in regard to which Board of Health regulations are so diverse, not to say occasionally unreasonable, as that of main traps. In some towns traps are required on drains connecting with cesspools, and prohibited on those connecting with a sewer; in others exactly the reverse is prescribed; in a third set drains of both sorts must be trapped; and a fourth set prohibits all traps.

Subsoil-overflows.

Fig. 16.

Main traps on drains.

Apart from the fancies of Boards of Health, a drain communicating with a cesspool is much better without a trap. Not only does the absence of the trap remove the source of many overflows of sewage into the basement, and consequent contamination of the house, but it allows free passage of air from the cesspool, which, in such cases, should have a perforated cover, through the house-drain and soil-pipe to the outlet of the latter above the roof. As the air in the cesspool, particularly if it has a perforated cover, is much better than that in the house pipes, lined, as the latter always are, with putrefying slime, the ventilation of the cesspool through the house system tends to purify and aerate the latter, without the slightest risk, if the cesspool is used by only one family, of introducing into the house any germs or infection not already existing in the house pipes; at the same time that, by causing a flow of air downward, through the perforated cover into the cesspool, by means of the strong draught existing in the warm pipes of the house, and thence through the house pipes to the roof, it prevents the smells usually noticed around a cesspool without such ventilation.

Where the house-drain connects with a public sewer, there is a reason for cutting off the access of air from the sewer to the house pipes by means of a trap, in the fact that the sewer contains infectious wastes from many diseased persons, and that, although sewer air has been many times proved to be remarkably free from floating microbes, there is reason to think it may, if inhaled, produce in the system a condition of predisposition to infection from certain causes. Of late years, however, while house systems of waste-pipes are better inspected, and made more secure against leakage of air, than formerly, the practice of engineers in building sewers has been modified, and the free ventilation now adopted has materially changed the character of sewer air. In many towns and cities the use of main traps on house-drains connecting with sewers is prohibited, for the express purpose of allowing the sewers to ventilate through the house pipes; and where the main trap is still insisted upon, the sewers are generally ventilated by open manhole covers in the streets. It is hardly necessary to say that an incautious person, passing one of these open manhole covers, is quite likely to inhale a larger dose of sewer air than he would get by living years in a house without a main trap; so that, as sewers are now built, the risk of infection from them is lessened, rather than increased, by leaving out all main traps, and utilizing the soil-pipes of the houses as ventilation flues, drawing fresh air in at the open manhole covers; while the danger and annoyance resulting from the almost inevitable choking of main traps are avoided.

Sewer-traps.

Where the trap exists, it is, or should be, always accessible, either from the inside of the house, or by a manhole outside, so that it can be cleaned out through the hand-hole. In most houses this operation must be repeated every few months, as the dip of the trap collects sediment, and, as the flow of warm, greasy water is checked by the bend, the grease chills and adheres to its sides. Warning is usually given of the approaching stoppage of the trap by the slow running off of water from the wastes of the basement fixtures, and it should then be cleaned at once, before a complete stoppage causes an overflow into the basement.