=Traps.=--The waste pipes from the wash basin and bath tub are always provided with some form of trap, to prevent air from entering the room from the sewer, charged with offending odors. Traps are made in many forms, but the purpose of all is to prevent the escape of sewer gas. The plain trap _S_, shown in Fig. 95, is that used under the basin in Fig. 91. It makes a tight joint by means of the nut _B_ and a rubber washer as in the case of other joints of the kind. The parts _C_ and _E_ are unions that permit the pipe or bowl to be removed without disturbing the remainder of the plumbing. From the form of the trap it will be seen that the U-shaped part below the dotted line _F_ will always remain full of water and so prevents the escape of air from the sewer. In case the trap becomes stopped the obstruction will likely become lodged in this part of the pipe. To clean the trap the screw-plug _D_ is taken out with a pair of pliers and the obstruction removed with a wire. The traps used in Figs. 90 and 92 are the same in principle as Fig. 95 but are made to discharge into a pipe placed in the wall instead of under the floor. The trap in Fig. 94 is a form known as the bottle-trap that is sometimes used in the more expensive plumbing. [Illustration: FIG. 95.--The S trap of nickel-plated brass tubing.] [Illustration: FIG. 96.--The Bower non-siphoning trap.] [Illustration: FIG. 97.--The drum type of non-siphoning trap.] [Illustration: FIG. 98.--An S trap made of lead pipe.] Another style much used with lavatories is the Bower trap shown in Fig. 96. In this trap the water comes down the pipe _B_ and pushing aside the hollow rubber ball _A_, enters the space surrounding it and is discharged at _C_. The ball, being light, is held against the end of the pipe by the water and acts as a stopper to prevent evaporation from taking place. Open traps, such as Fig. 95, if left standing for a long time, may lose sufficient water by evaporation to destroy the water seal and allow the sewer gas to escape. In the use of the Bower trap such occurrence is much less likely to take place. Fig. 97 is another trap much used on sinks; it is known under the trade name of the Clean Sweep trap. The part _C_ is much larger than the common trap and the water seal is less likely to be broken. The clean-out is larger and the interior is easy of access in case of stoppage. The simplest and most commonly used trap in cheap plumbing is that of Fig. 98. It is a lead pipe bent in the form of an _S_. It is the same in shape as Fig. 95 and performs its work as well but does not have the means of detachment shown in the latter. Traps of many other forms are in use but all have the same function to perform and the mechanical make-up is much the same as those described. [Illustration: FIG. 99.--A method of bath-room plumbing using the drum trap.]