resh-air inlet" is, as its name implies, an inlet for
fresh air. It is placed directly on the house side of the main
trap. The connections made vary considerably. A few good
connections in common use are explained below.

When the trap is in place, one of the clean-outs can be used for
the fresh air. If this is done, a Y-branch should be placed in the
hub of the clean-out. The Y-branch should be used for the fresh air
and the run should be used for a clean-out.

A Y-fitting can be inserted directly back of the trap and the
branch used for the fresh air. An inverted Y makes a good fitting
to use directly back of the trap. These branches should be taken
off the top of the pipe. The branch taken off for the fresh-air
inlet should not have any waste discharge into it and should not be
used for a drain pipe of any description.

The fresh-air inlet should run as directly as possible into the
outer air, at least 15 feet from any window. The pipes terminate in
a number of different ways, some with a return bend, above the
ground, some with a cowl cap, some with a strainer. When necessary
to run pipe through the sidewalk, a box of brick is made with a
heavy brass strainer fitted level with the sidewalk into which the
pipe runs. If the pipe is run into the box on the side a little up
from the bottom, the possibility of becoming stopped up or filled
up is not great. The fresh-air inlet sometimes terminates above the
roof of the building.

Special care should be given this fresh-air inlet as it supplies
fresh air to the entire system and thus keeps the pipes in a much
better sanitary condition.

Sometimes when the house drain is full of sewage, air is pushed out
of the fresh-air inlet and disagreeable odors are evident. This is
why it should be located as far as possible from any window.
Special care should be taken on the part of the plumber not to
locate the fresh-air inlet nearer than 15 feet to the fresh-air
intake of the heating system.

[Illustration: FIG. 60.--Fresh-air inlet.]

When the pipe passes through the foundation wall, the same care
should be exercised as with other pipes. That is, if the pipe is 4
inches, a sleeve 6 inches should be cut in the wall for the 4-inch
pipe to pass through.

POINTS TO REMEMBER ABOUT FRESH AIR.--

_First_, never should be smaller than 4 inches.

_Second_, one size smaller than trap.

_Third_, location, directly back of trap.

_Fourth_, leads to outer a