"wash-out" closets, so called, with the allied forms of "short hoppers" and "long hoppers," and the complicated and dangerous "plunger," "valve," and "pan closets," all depend on the 
Fig. 10.—"Short-Hopper" Water-Closet, showing Accumulations of Filth in the Bowl. weight of a stream or body of water falling from above to force out the waste matter from the bowl of the closet through the trap below. This force is rarely sufficient to give proper flushing action, even with a shallow trap-seal. A deeper trap would oppose too much resistance to the discharge of waste matters from closets of the kind just referred to. Cleanliness and safety can be secured only by a greatly modified form of construction, and by the employment of totally different means for flushing. The principles of the siphon and of the water-jet have been applied successfully to this purpose, so that deep and safe water-seals can be used which are in full view at all times.
The illustration, Fig. 11, shows a form of siphon closet devised by Colonel Waring. The flushing is effected by opening a valve in 
Fig. 11.—A Siphon Closet, with Deep Water-Seal. a tank above, which produces a quick rush of water into the bowl. This fills the longer arm of the siphon and the weir-chamber below by the overflow through the neck or short arm. As soon as this takes place, the contents of the bowl are forcibly drawn out by siphonic action and discharged into the waste-pipe, after which the normal level of the water in the bowl is re-established by an after-fill from the tank.
There are, however, certain so-called pneumatic or siphon closets which should be carefully avoided on account of their having a double trap. This principle of construction is directly
