31. In cities, drainage by regular sewerage is provided, but in the country, cesspools are usually built to receive the sewage from the building.

In many cases the old leaching cesspool, or dry well, is still adopted. If the house is to be supplied with water from a town or city service, or from springs higher than the building, and at a considerable distance, the leaching cesspool may be tolerated, on account of its low cost, but only so long as the circumstances require. If, however, water is to be drawn for use from any well within 300 feet of the proposed cesspool, and on the same or a lower level, no cesspool should be built that will allow its contents to soak into the subsoil.

32. If there is no danger that the drinking water may be contaminated, the cesspool may be excavated in a circular form from 8 to 12 feet in diameter, and usually of a depth sufficient to reach an absorbent stratum, the sides being lined with a dry wall of stone or brick, and the top drawn over in the shape of a rude dome, which should be covered either with an iron cover or a flat stone. In sandy or gravelly soils, such a cesspool will dispose of the waste liquids of the house for a long time, but in the course of years the earth around it becomes permeated with the solid matter in the sewage, and a new cesspool should be dug.

In very clayey soils no leaching or absorption of the sewage by the soil takes place, and the cesspool fills up like a tight cistern, one of ordinary size overflowing after a few days' use.

As the simplest way of getting rid of the sewage when the cesspool is full, is to pump it out at intervals through a hole in the cover, it is well to make proper provision for this when the cesspool is built.

33. To avoid the choking of the house drains by the filling of the cesspool, it is customary to provide an overflow through which the liquid can, if necessary, escape over the surface of the ground.

An automatic arrangement may be used instead of a surface overflow, consisting of a permanent outlet, formed by a series of open-jointed pipes, laid 8 or 10 inches beneath the surface; the liquid exuding from between them will be absorbed, partly by the porous loam which always forms the upper stratum, and partly by the roots of grass or other vegetation.