=155. Disposal of Waste in Cities.= In some cities, householders are required by law to have catch basins connected to their sewer systems to remove leaves and dirt from storm water and grease from kitchen sinks and laundry tubs. The laws of other cities forbid the use of catch basins, but urge householders to help care for the city sewer system by not putting grease into sewer pipes. Strong chemicals should not be put into the pipes. Use only boiling water in cleaning pipes. Do not wash vegetables on which there is much loose dirt in sinks. CHAPTER XXII WATER CLOSETS =156. Construction of Water Closets.= The water closet is a device for the disposal of excrement. The closet includes a tank of water for flushing the waste from the bowl to the sewer or waste pipe. Between the bowl and the waste pipe is a device called a trap which holds water and seals the end of the waste pipe so that gases from the sewer or the septic tank cannot come into the house. (Fig. 83-_a_.) The bowl of the newer models of water closets have the trap as a part of the bowl, which saves joints and connections likely to catch dirt and stop up the trap (Fig. 83). The water coming from the flushing tank is carried around the bowl so that it is flushed clean by the swift-flowing water. When the water reaches the bottom of the bowl, it rushes upward a few inches before it can turn downward to the waste pipe. This it does while flowing rapidly and cleansing the bowl; when the tank empties, water collects in the bowl to the level, where it can flow down the waste pipe (Fig. 83). As soon as all the water above this level has gone down the pipe, the remainder stays in the bowl, forming the seal until the next time the bowl is flushed. Fig. 83-_a_ shows two kinds of traps. If water flows at too rapid a rate thru the trap of the bowl, as in cases when there is too much pressure on the water or the tank is set too high so that gravity gives it too much force, or if an excessive suction is produced in the drain pipe, all the water may run out of the bowl, leaving the trap unsealed. The remedy for this is a change in the flushing tank or in its position. [Illustration: FIG. 83. Section of water closet.] =157. Siphoning the Trap.= If rags or shreds of material are dropped into the bowl and lodge in the trap, only a part of them going over into the waste pipe, they may siphon the water, sealing the trap, over into the waste pipe. There was more difficulty of this sort with traps of older models than with the newer types. Always leave clean water in the trap. [Illustration: FIG. 83-_a_. Types of traps.]