=Syphonic water-closets= are wash-down closets, in which the flushing out is aided by syphonic action. They need to be fitted with a flushing cistern, giving an after-flush as well as a flush; otherwise the basin is left untrapped. One of the most elaborate closets of this type is Jennings’ Closet of the Century. Fig. 27 shows that the flushing cistern has two connections with the closet, one in the usual manner with the flushing rim of the pan, the other connected to the long arm of the syphon (A Fig. 27). B is a puff pipe allowing the escape of air from this syphon when started. Thus while one part of the flush scours the basin, the other expels the air from A through the puff-pipe B, fills both arms of the syphon with water, and thus starts the syphonic action by which all the contents of the basin are sucked out of it. In this form of w.c., syphonage is intended to be produced, and the after-flush prevents the w.c. from being left untrapped. [Illustration: FIG. 26. WASH-OUT CLOSET.] [Illustration: FIG. 27. SYPHONIC CLOSET.] Syphonic water-closets appear to me to be unnecessarily elaborate and complicated, and the only advantage over the wash-down closet is the deeper layer of water in the basin. With a well-shaped wash-down closet this is of little importance. In other forms of wash-down w.c., =unsyphoning= may also occur, for instance, by pouring the contents of a slop-pail into the pan. This is particularly apt to occur, when two or three water-closets are on different floors of a house, one over another. This unsyphoning is prevented in the case of the highest w.c. by the soil-pipe ventilator, but not always for the lower w.c.’s. For these it may be necessary to carry a pipe from the highest point of the trap of the closet, where it joins the soil-pipe, through the wall into the external air. Such a pipe is called an _anti-syphonage pipe_ (Fig. 28). It effectually prevents the water being sucked out of the trap of a lower w.c. when the w.c. on a higher floor is being flushed. [Illustration: FIG. 28. A—Elevation. B—Section through wall of house, showing connection of w.c.’s on three floors, with soil-pipe and anti-syphonage pipe. _b_—Junction of closet trap with soil-pipe, _a_ being a P and _b_ an S trap. _c_—Junction of soil-pipe with earthenware drain. _d_—Anti-syphonage pipe, seen best in elevation A. _e_—Soil-pipe. _f_—Anti-syphonage pipe. _g_—Underground drain. _h_—Soil-pipe ventilator. _i_—Cage-work protecting top of _h_. _j_—Point at which anti-syphonage pipe is connected with soil-pipe ventilator, above the highest w.c.]