recommended. A diaphragm sludge pump is best suited for removing the tank contents that should be transported in a watertight, closed container. Trucks are made that specifically pump and carry the waste material to a place where it can be disposed of.

Tile Fields

Tile fields of lines made of concrete, clay, or PVC are laid in the ground with open joints or perforations to dispose of settled sewage into the ground. A fiber pipe (Orangeburg Alkacid) or plastic pipe with holes bored in the lower portion of the pipe to allow drainage may be used for these drain lines. This pipe is light in weight and is easily laid in the trench. It comes in sizes ranging from 2 inches to 8 inches in diameter and in lengths from 5 feet to 8 feet. Because of these long lengths, this type of pipe is particularly valuable in soil where other types of pipe may settle unevenly. Figure 2-14 shows a typical field layout.

PROPER FUNCTIONING. - The following conditions are important for proper functioning of tile fields:

Groundwater well below the level of the field

Soil of satisfactory leaching characteristics within a few feet of the surface, extending several feet below the tile

Subsurface drainage away from the field

Adequate area

Freedom from possibility of polluting drinking water supplies, particularly from shallow dug or driven wells in the vicinity

TESTS. - The length of tile and details of the filter trench generally depends upon the character of the soil. Soil leaching tests should be made at the site, as described for leaching cesspools, except the test hole should extend only to the approximate depth at which the tile lines are to be laid. For extensive tile fields,

Figure 2-14. - Typical layout of a subsurface tile system.