The best type of water closet yet designed, is the siphon-jet closet shown in section in Fig. 144. This closet is vitreous, smooth, impervious and contains a large body of water in a receptacle so shaped that it cannot easily be soiled. In operation it is almost noiseless. The operation of a siphon-jet closet is as follows:

The flushing water parts upon entering the closet; some of it enters the flush rim and cleanses the bowl, while the rest of it flows through the jet, a, and ejects the water from the closet. The ejected water enters the outlet leg, b, of the closet which is usually rifled,

Fig. 143 choked, or in some way has a constricted outlet that can be easily filled with water. When the outlet leg becomes filled it acts as the long leg of a siphon, and thus siphons the contents of the bowl into the soil pipe. Once the siphonic action is started it continues until the bowl is empty and enough air has entered the pipe to prevent further siphonage. The closet is then refilled by the after-wash from the tank or flush valve.

Fig. 144

As the contents of a siphon-jet closet are ejected by the pressure of the atmosphere on the surface of the water in the bowl, it follows that a considerable volume of air from in and around the closet will be carried into the soil pipe at each discharge, thus carrying off the most impure air from around the closet.