lock it can be removed. Sometimes vitrified
tile with cemented joints is used instead of cast-iron pipe; but it
has the distinct disadvantage that, if the rootlets of trees or large
shrubs, attracted by the water, find so much as a pin hole in the
cement, they will grow through and finally clog the pipe.

From the tank to the disposal field, the first three or four lengths
of pipe should be glazed tile with tight cement joints. From these on,
three or four inch porous land tile laid in shallow trenches is used.
For proper action, the trenches of the field should be not over
eighteen inches deep so that the warmth and evaporation of the sun may
be effective. Also in digging these trenches, there should be a slight
grade away from the outlet of the tank. An inch to every ten feet is
adequate.

The bottom of the trenches is covered with a two-inch layer of
medium-sized crushed stone or clean gravel. On this rest the land
tile, and the joints are covered with roofing paper to prevent bits of
stone or gravel from lodging within the pipe. The latter is covered
two inches deep with more stone or gravel and over all go lengths of
roofing paper cut slightly wider than the trench so that, when in
place, the paper arches and fits tightly to the sides. The purpose of
the stone or gravel is to facilitate water seepage from tile to ground
while the roofing paper cover prevents silt from reducing the seepage.

At the terminus of each trench is a leaching pool, built by digging a
hole about three feet across and five feet deep. It is filled with
crushed stone or small rocks to the level of the trench piping. Over
it, before replacing the dirt, goes another piece of roofing paper.
Into these pools drain what water has not seeped away in flowing from
the tank.

As can be seen from the foregoing description, the fermentation and
bacterial action that takes place in a properly built septic tank
system is automatic and needs no attention, although every second or
third year it is advisable to remove the mud-like sediment from the
tank. Otherwise, the latter's capacity gradually diminishes.

The steps involved in building such a system are so simple that, while
the services of a plumber are advisable, it is possible for an
intelligent handy man to do the work. Be sure, however, that he
realizes that each step is important and necessary. We knew of one
otherwise capable workman who calmly omitted the crushed stone and
gravel in the tile