3. =Plunger-closets=, of which the Jennings closet (Fig. 18) may be taken as a type. The handle lifts a plug, which allows the contents of the bowl to run out, and, when the plug is dropped in place, the bowl is filled again from a ball-cock. These closets are liable to get out of order; the plungers or plugs lose their rubber flanges and leak, and the plunger-chamber is apt to retain filth. [Illustration: Fig. 18.—Jennings closet.] 4. It is evident that if the hopper-closet could have its trap bent to one side out of sight, and its hopper enlarged toward the bottom, so that nothing would strike and cling to its sides, it would be an excellent one. Of such a type are the Tidal-Wave and National closets (Fig. 19), _a_ being the water-pipe, which discharges into a flushing rim, and _b_ a vent-pipe to relieve pressure between the two bodies of water during a discharge, and prevent siphoning. [Illustration: Fig. 19.—Tidal-wave closet.] [Illustration: Fig. 20.—Y-branch.] [Illustration: Fig. 21.—Quarter bend.] A water-closet, to be well flushed, should have a discharge of three gallons of water in five seconds, sent directly downward all around the rim. =School-sink= (also called trough-sink or privy-sink). An iron trough, having a sewer-connected opening with a movable iron plug in the bottom at one end, for the discharge of its contents, and a pipe at the other end, from which it is filled with water. It is practically an elongated water-closet. (See 53.) 12. =Y-branch= (Fig. 20), so named from its shape. There are also half Y-branches. =Eighth bends.= There are also quarter bends (Fig. 21), sixth bends, and sixteenth bends. These are used in pipe-connections in order to discharge the contents of the branch pipes in the same general direction with the current in the main pipes, for, if the discharge enters at a right angle, a deposit is apt to form opposite the point of connection.