, as it is within easy access. This can be done
without difficulty.

[Illustration: FIG. 41.--Inserting length of pipe.]

While laying the pipe a stopper is used to prevent the sewer gases
and foul odors from escaping. This stopper sometimes is of tile,
sometimes a plug of paper or burlap. This stopper is sometimes
cemented in by inexperienced men and the trouble created can only
be guessed at. If a stopper is used, the workman must see that it
is taken out.

REFILLING.--After the pipe is laid and cemented, it should be
covered and allowed to stand 24 hours to give the cement time to
harden. The dirt should then be thrown in and settled by means of a
tamper or by flooding with water. The planks should not be taken
out until the trench is well filled. To pull the plank, a chain or
shoe and lever will have to be used. Where the tunnels are, dirt
will have to be rammed in with a long rammer, care being taken not
to disturb the pipe. If the refill is not well rammed and tamped,
the trench will settle and cause a bad depression in the street
surface.

TERRA-COTTA PIPE.--Terra-cotta pipe should be straight, free from
fire cracks, and salt-glazed. The inside of the hub and outside of
the plain end should not be glazed. This allows the cement to take
hold.

TABLE OF STANDARD TERRA-COTTA PIPE

------+------------+-----------------+----------+--------------
Size | Thickness, | Weight per ft., | Depth of | Annular space
| inches | pounds | socket |
------+------------+-----------------+----------+--------------
3 | 1/2 | 7 | 1-1/2 | 1/4
4 | 1/2 | 9 | 1-5/8 | 3/8
5 | 5/8 | 12 | 1-3/4 | 3/8
6 | 5/8 | 15 | 1-7/8 | 3/8
8 | 3/4 | 23 | 2 | 3/8
9 | 13/16 | 23 | 2 | 3/8
10 | 7/8 | 35 | 2-1/8 | 3/8
12 | 1 | 45 | 2-1/4 | 1/2
15 | 1-1/8 | 60 | 2-1/2 | 1/2
18 | 1-1/4 | 85 | 2-3/4 | 1/2
20 | 1-3/8 | 100 | 3 | 1/2
------+------------+-----------------+----------+--------------

Terra-cotta pipe should not be permitted in filled-in ground.

Roots of trees find their way into the pipe through cracks or