Back-air pipes run along each upright line of soil or waste pipe, and for office washstands are 4 inches in diameter (except 5 inches where there are water-closets on the line). Vent pipes for urinals, basins, and slopsinks in toilet-rooms are 4 inches in diameter, and along soil pipes are 5 inches in diameter. All back-air lines run through the roof independently, and are dripped at the bottom of the line, and all T branches for vents from fixtures are set above the overflow point of the fixture so that the vent line cannot act as a waste pipe in case of stoppages.

Branch waste and vent pipes and flush pipes for fixtures are drawn *'D" lead pipes, weighing as follows:

All water-closet lead bends are of eight-pound lead. In all toilet-rooms, whether public or private, except those for employees and janitors, all exposed waste, vent, and flush pipes are of heavy seamless drawn brass heavily nickel-plated. All back-air pipes for traps, as far as exposed to view, including couplings, etc., are of heavy seamless brass, nickel-plated. All safe waste lines are of galvanized wrought iron. 1½ inches inside diameter, all put together with screw joints, and with 1½ x 1- inch branches for outlets in safes on each floor. All drip-pipe lines are carried independently at the ceiling of the cellar and made to discharge through finished hinged brass flap valves separately and openly into a trapped and water-supplied sink in the cellar. Along each vertical line of soil pipe and waste pipe is a line of 1½ -inch drip pipe from the marble safes or platforms under the fixtures. These drip pipes are carried down to the engineer's sink in the pipe cellar, each line separately, and the mouth of each is protected by a stamped brass-hinged flap valve. Waste-pipe lines for office washstands are 3 inches in diameter (except 5 inches where there are water-closets on the line). Waste pipes for urinals, basins, and slopsinks in toilet-rooms are 4 inches in diameter. All soil pipes are 5 inches in diameter.

The roof drainage is carried down through four 4 and one 6-inch extra-heavy asphalted wrought-iron inside leaders, each trapped at the foot of the stack by a full-size extra-heavy cast-iron trap, and connected by Y branches and eighth bends with the two sewer lines. All outside leaders for domes, skylights, etc. are connected with brass or copper ferrules and calked joints to the rainwater inlets in the wrought-iron leaders.

Figure 3 shows the arrangement and connections of the two 5,000-gallon roof tanks, which are located in a separate tank-house built on the main roof. Each tank rests on three rolled-steel girders, which distribute its weight over four lines of floor beams, and is made of boiler-iron, lap-riveted and stayed by 10 intersecting internal tie-rods. The tanks are 7 feet 6 inches deep, and are intended to hold 7 feet of water. The bottoms of the tanks are connected by a 3-inch flanged cast-iron pipe A with vertical ends, having gate valves B and D, through which the main house supply is drawn. Ordinarily it is intended that the tank W shall be filled with well water for use in flushing cisterns only, and tank C should be filled with city water for other general purposes. When this is the case valve D is closed and valve B is open, supplying the intermediate tanks, boiler, and riser lines through pipe A and its connections. Valve E is open to supply the special cistern system, and valve F is always open to insure a constant tank-pressure fire service. R is a check valve closing toward the tank with the pressure from the fire pump. By reversing valves B and D the whole supply may be taken from the well tank W, and by opening both of them the water in both will be mixed and equalized. G G are vent pipes to promote the emptying of the riser lines, and H H are copper floats operating the electric alarms indicating in the engine-room. The vertical outlet pipes at B and D rise 6 inches above the bottom of the tanks.