Householders have long been familiar with the fact that although solids contained in sewage may have been discharged for long periods of time into a cesspool, the latter, if located in dry, porous soil, did not seem to become filled with the solid residue. This is due to the liquefaction of the solid matter in the sewage after its discharge into the cesspool, and to the seepage and bacterial reduction of the liquid matter in the surrounding soil. To replace the cesspool and eliminate the insanitary conditions which, in most instances, result from its use, other methods have been devised which utilize the agencies of nature to the best advantage. Thus the sedimentation and, in some cases, the liquefaction of the solid matters in sewage are carried on in specially designed settling tanks which are easily cleaned and which provide for greater efficiency in settling out suspended matters than the cesspool. Similarly, the filtration of liquids from cesspools through the soil is replaced by the scientific method of sub-surface irrigation, which is much more efficient in three distinct ways: (1) the limited seepage area represented by the walls of the cesspool is increased many times by distributing the effluent from the settling tank over a large area of soil in a system of sub-surface tiling; (2) the bacterial reduction is more effective, since it has been found that the bacterial action necessary to purify sewage takes place in the upper layers of the soil and is almost absent at depths of five feet or more; (3) the soil is given an opportunity to rest and to dry out by alternately using different portions of the sub-surface irrigation system. In the cesspool the seepage of the effluent and whatever bacterial action takes place in the surrounding soil must go on continuously, which often results in clogging of the soil and overflowing of the cesspool. The purification and final disposition of sewage by means of sub-surface irrigation is the method best adapted to the single residence, and oftentimes to the hotel or institution, if soil conditions are favorable and proper area is available. This system requires less oversight in its operation than the various forms of artificial filters. Furthermore, the sewage is entirely hidden from sight after it leaves the settling tank, and this is usually desirable near private residences and on the grounds of country homes, country clubs, and summer hotels. Also, where the sewage must be treated in close proximity to a residence or hotel or at a point on the windward side of a residence, this method, more effectually than any other, precludes the possibility of a nuisance resulting from the operation carried on, since the settling-tank effluent is at no point exposed directly to the air. Furthermore, its cost is less than that of other works for final treatment of sewage, and, finally, the system is more easily installed.