The cesspool is made use of only in the absence of public sewers. Whenever entrance may be made into a public sewer, the use of the cesspool should be discontinued entirely. After public sewers have been constructed, cesspools are sometimes connected into the sewer instead of replacing them entirely, with a direct connection from house to sewer. This is extremely poor practice, for the cesspool should always be considered simply as a makeshift, made necessary by the absence of better facilities. The worst feature that presents itself in country plumbing, is the disposal of the soil in house sewage.
Plate XLVIII. Construction And Use Of Cesspools
Costruction of Cesspools
When, as occasionally happens, the sewage of a house may be discharged into a running stream, the difficulty may be solved in the case of that particular house, although for all points lower down on such a stream, the water is polluted and should not be used for drinking purposes. Therefore this method is usually out of the question, even though such a stream is at hand. The only other practical method is to discharge the house sewage into a tank, from which the liquids may escape into the surrounding soil, the tank retaining the solid matter, including soil. Such a tank or compartment is called a cesspool. In Plate 48 are shown two forms of cesspool, the leeching and combination leeching and tight cesspools. The former is by far the more common type. The leeching cesspool is built of loose brick or stone, without the use of cement. Through the crevices or joints in the sides of the cesspool, the liquids leech out into the surrounding soil, leaving the solid matter to remain in the cesspool. A serious objection to the use of this form of cesspool is that, after a time, the crevices become filled with soil and other solid matter, and the leeching process is interfered with. Another objection is that more or less solid matter passes off with the liquid into the surrounding soil, thereby in time destroying it as a filtering medium, upon the effectiveness of which, the proper action of the cesspool depends. To be sure, when these results have come about, the liquids entering the cesspool may be carried into a second cesspool through an overflow, in which case the first cesspool will continue to retain the solid part of the sewage, and the second cesspool to dispose of the liquids, somewhat in the manner of the septic tank.
When the first cesspool has become filled it may be emptied, and its use continued. Instead of discharging into one cesspool and overflowing into a second one, it may be more desirable, when the first cesspool is no longer able to perform its duties satisfactorily, to abandon it, disconnect the house drain from it and reconnect into a cesspool located in new soil.
The only proper location for a leeching cesspool is in light or sandy soil, into which the liquids may leech and purify themselves by filtration. Sand is a recognized filtering medium. Filtration depends upon the action of certain bacteria which exist in the soil, their numbers being far greater in light soils than in those which are heavier, as in the former, air has an opportunity to reach the bacteria, without which the bacteria are unable to live.
Therefore, at considerable depths, the action of filtration is not nearly so strong as at points nearer the surface, and for this reason, cesspools of comparatively small depth will give better service.
While the employment of the leeching cesspool in the manner described above is the common method, a better method is to discharge the house drainage into a tight cesspool and connect it by overflow into a second cesspool of the leeching type, the first retaining the solids, which may be cleaned out, and the second cesspool leeching the liquids into the surrounding soil. The water-tight cesspool should ordinarily be about six feet in diameter by ten feet in depth, and is usually built of brick, one brick thick, laid in Portland concrete, and provided with a 24-in. cast-iron cover and frame. A tight cesspool should not be located within two feet of any boundary line, or within ten feet of any house or rain-water cistern, or within thirty feet of any source of water supply. A leeching cesspool should not be located within 100 feet of any house or cistern, or within 300 feet of any source of water supply.
The house sewer should be trapped before entering a cesspool, and the trap provided with a 4-in. fresh-air inlet, which should be governed by the regular limitations surrounding the construction of fresh-air inlets. The cesspool, whether leeching or water-tight, should be vented by a 4-in. vent pipe, carried at least 10 ft. into the air. A convenient method is to carry this vent line on a stout pole or post, set for the purpose. The ground above the cesspool should be banked with turf, in order to shed surface water and prevent its entrance into the cesspool.
Rain water should not be discharged into a house sewer connecting with a cesspool, as the latter will be flooded and called upon to take care of drainage which is not harmful to discharge upon the surface of the ground if properly provided for. It will be seen that the leeching and water-tight cesspool each has its own particular advantages, which, in the main, are not held in common.
A most excellent form of cesspool, combining the features of these two types, is the combination leeching and tight cesspool shown in Plate 48, the construction and action of which are as follows:
An excavation of proper size having been made, a heavy layer of broken stone is filled into the bottom, and upon this as a foundation a common brick, water-tight cesspool is built, a wide space being left between it and the sides of the excavation, which space is filled with broken stone. Overflow outlets at several points around the cesspool, and exactly on the same level, are then constructed, which will allow liquids to pass over into the broken stone and leech into the soil, the heavy matter remaining in the water-tight cesspool, from which it may be removed at intervals. This form of cesspool takes up but little more room than an ordinary cesspool, is as efficient as the use of the tight cesspool overflowing into a leeching cesspool, and is in every way a very satisfactory arrangement for handling the drainage of a country house. The outlets should be on the same level, in order that the liquid may be distributed evenly into the broken stone.
If these outlets are not placed on the same level, the lower ones will get nearly all the waste from the cesspool, and that part of the filtering material into which they discharge will after a time become filled with impurities, and thus be unfit to perform the duties required of it; whereas, if each outlet is made to take care of its proportional part of the work, the cesspool can be made to do good work for a much longer period.
Notwithstanding that the main part of the solid matter remains in this cesspool, a small part at least of the solids is carried out into the broken stone. Instead of outlets of the style shown in Plate 48, very good outlets may be obtained by using half-S lead traps in an inverted position.
The sewage should be brought into the cesspool in such a way that its contents will not be stirred up any more than possible.
If the contents are disturbed, a greater amount of solid matter will be carried out through the overflows. By carrying the inlet pipe well down into the cesspool, the sewage will enter with less commotion than otherwise.
While there is a great difference between the efficiencies of the several types of cesspools, it should always be remembered that this device at best is only made use of as the most practicable method of solving a difficult problem, at the least possible expense. In other words, the cesspool should be considered only as a necessary evil, to be used only when other methods cannot be employed.
City plumbing ordinances make acknowledgment of this fact by prohibiting the use of cesspools in all sections of the city that are provided with public sewage facilities. A very great improvement over the cesspools, as shown in Plate 48, is to be found in the septic tank.
This subject is one of very great importance, and is taken up under the following plate.