few
stringers and braces to support it. When only a few planks are used
the term "corduroy the bank" is used (see Fig. 37).

[Illustration: FIG. 37.--Arrangement of plank for gravel.]

ROCK.--Where rock is encountered, blasting is resorted to. The
plumber should not attempt to handle a job requiring the use of
powder. It is dangerous in the hands of a person not used to
handling it and the work should be sublet.

A sketch of the two methods above for planking trenches is given
and a little study will make them clear.

LAYING OF PIPE

The pipe should be laid on the bottom of the trench to a pitch of
at least 1/4 inch per foot fall. In laying, the start should be
made at the street sewer with hubs of pipe toward the building. The
trench should be dug within a few inches of the bottom of the
pipe, then as the pipe is laid the exact depth is dug out, the
surplus dirt being thrown on the pipe already laid. The body length
of pipe should be on solid foundation. A space dug out for each hub
as shown in Fig. 38 allows for this, also allows for the proper
cementing of joints. To get the proper pitch of pipe, take for
example 1/4 inch per foot, a level 2 feet long with a piece of wood
or metal on one end 1/2 inch thick will answer. The end with the
1/2-inch piece on should be on the lower hub and the other end
resting on the hub of the pipe about to be put in place. When the
bubble shows level, then the pipe has the 1/4-inch fall per foot.
If a tile trap is used, it should be laid level, otherwise the seal
will be weakened or entirely broken.

[Illustration: FIG. 38.--Laying terra-cotta pipe.]

CUTTING.--The cutting of tile is not difficult, but must be done
carefully or the pipe will crack or a piece will be broken out,
thus making the pipe worthless. To cut tile or terra-cotta pipe,
stand the pipe on end with the hub down, fill the pipe with sand to
the point of cutting. With a sharp chisel and hammer cut around the
pipe two or three times and the pipe will crack around practically
straight.

CEMENTING.--If the pipe is free from cracks, the only possible way
roots can get into the inside of terra-cotta pipe is through the
cement joint. There are two ways of making these joints. Both ways
are explained below and are used today on terra-cotta work.

_First._--The bottom of the hub of pipe in place is filled with
cement and the straight end of the next piece of pipe is laid in
place, then more cement