=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. All soil and waste pipes must, whenever necessary, be securely fastened with wrought-iron hooks or straps. Vertical soil and waste pipes must not be trapped at their base, as the trap would not serve any purpose, and would prevent a perfect flow of the contents. =Branch Soil and Waste Pipes.=--The fixtures must be near the vertical soil and waste pipes in order that the branch waste and soil pipes should be as short as possible. The trap of the branch soil and waste pipes must not be far from the fixture, not more than two feet from it, otherwise the accumulated foul air and slime in the waste and soil branch will emit bad odors. The minimum sizes for branch pipes should be as follows: Kitchen sinks 2 inches Bath tubs 1-1/2 to 2 " Laundry tubs 1-1/2 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."