2 to 2 "
Water-closets not less than 4 "

Branch soil and waste pipes must have a fall of at least one-quarter
inch to one foot.

The branch waste and soil pipes and traps must be exposed, accessible,
and provided with screw caps, etc., for inspection and cleaning
purposes.

Each fixture should be separately trapped as close to the fixture as
possible, as two traps on the same line of branch waste or soil pipes
will cause the air between the traps to be closed in, forming a
so-called "cushion," that will prevent the ready flow of contents.

"All traps must be well supported and rest true with respect to their
water level."

=Vent Pipes and Their Branches.=--The purpose of vent pipes, we have
seen, is to prevent siphoning of traps and to ventilate the air in the
traps and pipes. The material of which vent pipes are made is cast
iron.

The size of vent pipes depends on the number of traps with which they
are connected; it is usually two or three inches. The connection of
the branch vent to the trap must be at the crown of the trap, and the
connection of the branch vent to the main vent pipe must be above the
trap, so as to prevent friction of air. The vent pipes are not
perfectly vertical, but with a continuous slope, so as to prevent
condensation of air or vapor therein.

The vent pipes should be extended above the roof, several feet above
the coping, etc.; and the extension above the roof should not be of
less than four inches diameter, so as to avoid obstruction by frost.
No return bends or cowls should be tolerated on top of the vent pipes.
Sometimes the vent, instead of running above the roof, is connected
with the soil pipe several feet above all fixtures.

[Illustration: FIG. 23.

LEADER PIPE.]

=Rain Leaders.=--The rain leader serves to collect the rain water from
the roof and eaves gutter. It usually discharges its contents into the
house drain, although some leaders are led to the street gutter, while
others are connected with school sinks in the yard. The latter
practice is objectionable, as it may lead the foul air from the school
sink into the rooms, the windows of which are near the rain leader;
besides, the stirring up of the contents of the school sink produces
bad odors. When the rain leader is placed within the house, it must be
made of cast iron with lead-calked joints; when outside, as is the
rule, it may be of sheet metal or galvanized-iron pipe with soldered
join