pply distribution within the house. While the former is not
absolutely essential, as a house may have a system of plumbing without
there being a sewer in the street, still in the water-carriage system
of disposal of sewage the street sewer is the outlet for the various
waste and excrementitious matter of the house. The house-water
distribution serves for the purpose of flushing and cleaning the
various pipes in the house plumbing.

The purposes of house plumbing are: (1) to get rid of all excreta and
waste water; (2) to prevent any foreign matter and gases in the sewer
from entering the house through the pipes; and (3) to dilute the air
in the pipes so as to make all deleterious gases therein innocuous.

To accomplish these results, house plumbing demands the following
requisites:

(1) _Receptacles_ for collecting the waste and excreta. These
receptacles, or plumbing fixtures, must be adequate for the purpose,
small, noncorrosive, self-cleansing, well flushed, accessible, and so
constructed as to easily dispose of their contents.

(2) _Separate Vertical Pipes_ for sewage proper, for waste water, and
for rain water; upright, direct, straight, noncorrosive, water- and
gas-tight, well flushed, and ventilated.

(3) Short, direct, clean, well-flushed, gas-tight branch pipes to
connect receptacles with vertical pipes.

(4) _Disconnection_ of the house sewer from the house pipes by the
main trap on house drain, and disconnection of house from the house
pipes by traps on all fixtures.

(5) _Ventilation_ of the whole system by the fresh-air inlet, vent
pipes, and the extension of all vertical pipes.

=Definitions.=--The _House Drain_ is the horizontal main pipe
receiving all waste water and sewage from the vertical pipes, and
conducting them outside of the foundation walls, where it joins the
house sewer.

The _Soil Pipe_ is the vertical pipe or pipes receiving sewage matter
from the water-closets in the house.

The _Main Waste Pipe_ is the pipe receiving waste water from any
fixtures except the water-closets.

_Branch Soil and Waste Pipes_ are the short pipes between the fixtures
in the house and the main soil and waste pipes.

_Traps_ are bends in pipes, so constructed as to hold a certain volume
of water, called the water seal; this water seal serves as a barrier
to prevent air and gases from the sewer from entering the house.

_Vent Pipes_ are the special pipes to which the traps or fixtures are
connected by