ad supplies are run directly to the bib on a sink,
this joint is necessary. It becomes necessary to wipe in a piece of
brass for a brass-pipe connection from a lead pipe, in which case
this joint is called for.

THE DRUM TRAP.--The drum trap is used under sinks, baths, showers,
and trays.

CHAPTER VII

LAYING TERRA-COTTA AND MAKING CONNECTIONS TO PUBLIC SEWERS. WATER
CONNECTIONS TO MAINS IN STREETS

TERRA-COTTA PIPE

One of the first pieces of work which a plumber is called upon to
do, when building operations commence, is to run in the terra-cotta
sewer from the street sewer into the foundation wall.

[Illustration: FIG. 35.--Connection of house sewer to main sewer.]

When the street sewer is laid, Y-branches are left every few feet.
A record of the branches and their distance from the manhole is
kept generally in the Department of Sewers or Public Works.
Therefore, the exact measurement of any branch can be obtained and
the branch found by digging down to the depth of the sewer. A
branch should be chosen so that the pipe can be laid with a pitch,
the same way as the main sewer pitches. This can be done by getting
the measurements of two of these branches and choosing the one that
will serve best. When there is a brick sewer in the street and no
branches left out, the sewer must be tapped wherever the house
sewer requires it (see Fig. 35).

DIGGING TRENCHES.--After the measurements and location of the house
sewer and sewer branches are properly located, the digging of the
trench is started. The methods employed to dig the trench vary
according to the nature of the ground, that is, whether it is sand,
rock, or wet ground. A line should be struck from sewer to
foundation wall to insure a straight trench.

[Illustration: FIG. 36.--Laying of plank for trench dug in sandy
ground.]

SANDY GROUND.--If the ground is sandy, the sides of the trench will
have to be sheathed or planked and the planks braced so as to
prevent the bank caving in. As the trench is dug deeper, the planks
are driven down. When the trench is very deep, a second row of
planking is necessary. The planks must be kept well down to the
bottom of the trench and close together, otherwise the sand will
run in. It is well to test the planking as progress is made by
tamping the sand on the bank side of the planks.

GRAVEL.--Where the ground is mostly gravel and well packed, the
above method of planking is unnecessary. The bank should have a