The simplest method of operating the dosing tank is by means of a hand valve fastened either to the floor of the chamber or to the bottom of the outside wall. Fig. 10 shows a simple form of a valve suitable for the floor and intended to be operated by a rod extending up through the sewage to the outside air. Such a valve can be made at any local foundry, the bearing surfaces turned up in any machine shop, and a piece of leather for packing purchased at any hardware store. Such a design, however, is not suitable for a large valve or for a great depth of water, since the pressure on the valve is dependent on the weight of the column of water acting on its area. If the outlet pipe is six inches in diameter, the diameter of the upper surface of this valve would be about ten inches, and the area of the top of the valve would be about half a square foot, so that, with six feet of water above, weighing 62½ pounds per square foot, the weight on the valve to be lifted would be 186 pounds, rather more than could be lifted by one man. Under such conditions it would be necessary, using such a valve, to rig a lever, the fulcrum being fastened to the edge of the tank, the short end of the lever to the rod, and the long end so arranged as to reduce the load in the ratio of about one to four. Fig. 11 shows another type of valve intended to be set into the side of the tank with the floor sloping rapidly toward the low point at which this valve is set. These valves require better workmanship and are preferably purchased from one of the dealers in valves who make this type as one of their regular stock forms. Fig. 12 shows the design made by the Coffin Valve Company, of Troy, N. Y., and a similar form of valve is made by the Caldwell-Wilcox Company, Newburg, N. Y. For a six-inch pipe, these valves are so made that the danger of the moving parts rusting together is avoided by having one surface bronze or some similar noncorrosive metal. Fig. 13 shows an ordinary gate valve generally used for water works, but applicable to sewerage works. Such a valve is shown in Fig. 5. [Illustration: FIG. 12.—Sluice-Gate Valve made by Coffin Valve Co.] [Illustration: FIG. 13.—Ordinary Gate Valve.] Fig. 14 shows a form made in England and largely used as a cheap valve for the purpose of emptying a tank rapidly. The peculiarity of the valve is that a sidewise motion of the long handle locks the valve into position so that the moving part of the valve may be readily set at any height. The one shown in the figure is taken from the catalogue of the Adams Hydraulic Company, Westminster, London, and is listed in their catalogue at $6.50 for a six-inch pipe. [Illustration: FIG. 14.—English Slide Valve with Wedge-lock Handle.]