pipe, and render it unfit to
perform its duty, to be washed away into the sewer.

CROWN VENTING, Fig. 59, is as its name implies, a vent that is
taken from the crown of the trap, thence into the main vent.

Each one of these methods of venting is used and considered good
practice, provided it is properly installed and correctly connected
with the use of proper fittings.

[Illustration: FIG. 59.--Crown venting.]

THINGS TO REMEMBER.--

_First_, venting is to prevent traps from syphoning.

_Second_, also to allow free passage of air.

_Third_, circuit vent--loop vent.

_Fourth_, continuous venting.

_Fifth_, crown venting.

_Sixth_, ventilation pipe extends from the top of fixture through
roof.

CHAPTER XI

HOUSE TRAPS, FRESH-AIR CONNECTIONS, DRUM TRAPS, AND NON-SYPHONING
TRAPS

The _house trap_ is a deep seal trap placed inside the foundation
wall, and intersects the house drain and house sewer. The trap is
placed at this point for a number of reasons: first, to keep sewer
gases from entering the pipes in the house; second, this location
is where the house drain ends. This trap should have two
clean-outs, one on each side of the seal. The clean-outs should be
of extra heavy cast-iron body with a heavy brass screw cap. The cap
should have a square nut for a wrench to tighten or unscrew the
cap. This cap should be brought up flush with the floor. When a
house trap is being set, it is necessary to set it perfectly level,
otherwise the seal of the trap is weakened and sewer gases can
enter.

Sometimes the trap is located on the house sewer just outside of
the foundation wall. In this case, a pit should be built large
enough for a workman to get down to it to clean it out when
necessary.

_A mason's trap_ was formerly used to a considerable extent, but is
very poor practice to use today on modern work. This trap was built
square of brick with a center partition. The brick soon became foul
and the trap would be better termed a small cesspool than a trap.

POINTS TO REMEMBER ABOUT HOUSE TRAPS.--

_First_, should be a running trap.

_Second_, two clean-outs.

_Third_, deep seal, at least 2 inches.

_Fourth_, set level.

_Fifth_, set inside foundation wall.

_Sixth_, accessible at all times.

_Seventh_, same size as house drain.

_Eighth_, fresh air should connect with it.

FRESH-AIR CONNECTIONS

The term "f