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 house pipes; unfortunately most fresh-air inlets are constantly obstructed, and do not serve the purpose for which they are made.
The Soil and Waste Pipes.—The soil pipe receives liquid and solid sewage from the water-closets and urinals; the waste pipe receives all waste water from sinks, washbasins, bath tubs, etc.
The material of which the vertical soil and waste pipes are made is cast iron.
The size of main waste pipes is from three to four inches; of main soil pipes, from four to five inches. In tenement houses with five water-closets or more, not less than five inches.
The joints of the waste and soil pipe should be lead calked. The connections of the lead branch pipes or traps with the vertical lines must be by Y joints, and by means of brass ferrules, as explained above.
The location of the vertical pipes must never be within the wall, built in, nor outside the house, but preferably in a special three-foot square shaft adjacent to the fixtures, extending from the cellar to the roof, where the air shaft should be covered by a louvered skylight; that is, with a skylight with slats outwardly inclined, so as to favor ventilation.
The vertical pipes must be accessible, exposed to view in all their lengths, and, when covered with boards, so fitted that the boards may be readily removed.
Vertical pipes must be extended above the roof in full diameter, as previously stated. When less than four inches in diameter, they must be enlarged to four inches at a point not less than one foot below the roof surface by an "increaser," of not less than nine inches long.