The cesspool depends for its action upon seepage into the surrounding soil and consequently is particularly unsatisfactory in tight clay soils. In more open sand and gravel soils the seepage is reduced as the pores of the soil become clogged with particles of solids, until it stops entirely, and overflowing occurs. Emptying and then cleaning the walls and floor of a cesspool do not fully open up the clogged soil pores, and overflowing can be expected to occur soon again. Solids in cesspools must be removed from time to time by bailing or pumping and should then be buried 18 to 24 inches deep in a trench where the water supply will not be endangered. Caustic potash (lye) will to some extent liquefy solids in a cesspool. This treatment does not eliminate the necessity of removing the contents when periodic inspection shows that the cesspool is nearly full. Caustic potash converts the greases into soft soap, whereas caustic soda forms a hard soap that does not readily dissolve. The chemical treatment is not effective in liquefying solids in the pores of the soil surrounding the cesspool. [Illustration: Figure 13.--A neat, whitewashed lattice along the paved walkway provides protection from cold wind and rain and gives added privacy.] When clogging continues and cannot be corrected, in most cases the best solution to the problem would be to abandon the cesspool and install a septic-tank system with tile disposal field. The cesspool should be completely filled with stones, earth, or other solid materials to avoid possible cave-ins.[8] [8] See The Septic Tank, p. 8. PRIVIES A privy when safely located and properly built and maintained is satisfactory for its purpose on the farm. Privies should be built 50 to 150 feet from the farmhouse, preferably on the opposite side of the house from prevailing winds, and at least 50 feet from the well. A site downhill from the well is generally safest. In some cases, however, the ground water may flow in a direction opposite to the slope of the surface, in which case the privy should be built on the other side of the well. Direction of flow may sometimes be learned from soil surveys, well-driller's data, or other similar sources. A distance of at least 6 feet from fences or other buildings allows for proper mounding of the privy and keeps it away from roof drainage from adjacent buildings. Good, tight construction with screened ventilators keeps insects and birds from entering, prevents rapid deterioration of the building, and provides greater comfort for the user. Certain features, while not essential to sanitation and satisfactory service, add to personal convenience. A paved walkway, well protected from cold winds and rain, is desirable. A neat, whitewashed lattice, as shown in figure 13, an arbor covered with vines, or a hedge screen adds to privacy.