ded."

_Main Traps._--The disconnection of the house pipes from the street
sewer is accomplished by a trap on the house drain near the front
wall, inside the house, or just outside the foundation wall but
usually inside of the house. The best trap for this purpose is the
siphon or running trap. This trap must be constructed with a cleaning
hand-hole on the inside or house side of the trap, or on both sides,
and the hand-holes are to be covered gas-tight by brass screw
ferrules.

_Extension of Vertical Pipes._--By the main trap the house-plumbing
system is disconnected from the sewer, and by the traps on each
fixture from the air in the rooms; still, as the soil, waste, and
drain pipes usually contain offensive solids and liquids which
contaminate the air in the pipes, it is a good method to ventilate
these pipes. This ventilation of the soil, waste, and house drain
pipes prevents the bad effects on health from the odors, etc., given
off by the slime and excreta adhering in the pipes, and it is
accomplished by two means: (1) by extension of the vertical pipes to
the fresh air above the roof, and (2) by the fresh-air inlet on the
house drain.

By these means a current of air is established through the vertical
and horizontal pipes.

Every vertical pipe must be extended above the roof at least two feet
above the highest coping of the roof or chimney. The extension must be
far from the air shafts, windows, ventilators, and mouths of chimneys,
so as to prevent air from the pipes being drawn into them. The
extension must be not less than the full size of each pipe, so as to
avoid friction from the circulation of air. The use of covers, cowls,
return bends, etc., is reprehensible, as they interfere with the free
circulation of air. A wire basket may be inserted to prevent foreign
substances from falling into pipes.

_Fresh-air Inlet._--The fresh-air inlet is a pipe of about four inches
in diameter; it enters the house drain on the house side of the main
trap, and extends to the external air at or near the curb, or at any
convenient place, at least fifteen feet from the nearest window. The
fresh-air inlet pipe usually terminates in a receptacle covered by an
iron grating, and should be far from the cold-air box of any hot-air
furnace. When clean, properly cared for, and extended above the
ground, the fresh-air inlet, in conjunction with the open extended
vertical pipe, is an efficient means of ventilating the air in the