Overflow or waste-pipes from cisterns for drinking water or from cisterns for flushing w.c.’s or to safe trays under the seat of water-closets should all be made to discharge into the open air, where the leakage can at once be discovered. The form of gully-trap to be used at the junction with the drain is described on page 167. =Other Waste-pipes= as from bath, lavatories, and sinks, must be similarly disconnected from the drain, and made to discharge over gully-traps. When the pipe leading from the bath, lavatory basin, or sink, is long, it is apt to become foul from the accumulation on its inner surface of slimy matter, consisting of soap, dirt, and other offensive matter. For this reason it is wise to have a syphon bend in the waste-pipe near its junction with the sink or basin. Such a trap is shown in Fig. 19. The syphon bend alone in the waste-pipe without disconnection from the drain at its lower end would not suffice to ensure complete absence of nuisance, especially for sinks and lavatories which may be disused for a considerable period. Under these circumstances the water in the syphon trap may become evaporated, and then foul drain gases be wafted into the house. Furthermore, even if the water in the syphon trap remained, foul gases may be absorbed from the drain and given out at the end nearest the house (_a_, Fig 19). Hence it is always best to disconnect all waste-pipes from the drain, except the soil-pipe which cannot be treated in this way. The waste-pipe from the upstairs lavatory or bath may be made to discharge over a hopper-head and thence into the rain-water pipe, which is disconnected below from the drain. This plan should only be adopted when the hopper-head is not close to a bedroom window. [Illustration: FIG. 19. SYPHON TRAP UNDER SINK, WITH SCREW-OPENING FOR CLEANSING.] Under the bath is usually placed a leaden tray, called a _safe_, to catch any accidental spillings of water. The overflow pipe from this safe should discharge direct into the open air. Formerly much evil was caused by allowing waste-pipes from baths, sinks, and lavatory-pipes, or overflow pipes from drinking-water cisterns or from the bath-safe, to be connected directly either with the trap of the w.c., or with the soil-pipe beyond it. [Illustration: FIG. 20. A. STONEWARE GULLY-TRAP. B. SECTION OF THE SAME, SHOWING A WATER-SEAL 3 INCHES IN DEPTH.]