Odors from privy pits and vaults can be reduced by covering the contents with dry earth, ashes, manure, or sawdust. These materials fill up the pit rather quickly, but can be used where other deodorants are not available. Sometimes two cakes of yeast dissolved in 2 gallons of water are effective in reducing odors. Commercial deodorants are available from suppliers of disinfectants. If a person in the family has typhoid fever or is a carrier of that disease or has dysentery, it is advisable to disinfect the excreta. Fire, live steam, boiling water, and such chemicals as caustic soda (sodium hydroxide), caustic potash (potassium hydroxide), or hypochlorite or chloride of lime may be used. The heat generated by the slacking of quicklime is also effective. Best results are obtained if the infected material is treated prior to depositing it in the privy. Further advice may be obtained from physicians, local health officers, or State health departments. CHEMICAL CLOSETS In general, chemical closets should be used only where there are elderly or infirm people unable to get outdoors, particularly in winter-time. In some localities their use is forbidden by law because of improper maintenance. Strict adherence to the manufacturer's directions for making the installation is necessary to obtain satisfactory service. The chief advantage of chemical closets is that they may be within or adjoining the house and used without regard to soil or ground-water conditions. The caustic chemicals required, if used properly, reduce the quantity of solid matter by liquefying action, disinfect and deodorize the contents, and lessen danger from flies. Disadvantages are the cost of the chemicals and necessity for careful and constant maintenance. The chemical-tank closet is generally recommended rather than the dry-type chemical closet. Three variations of tanks are available commercially. One type contains a clean-out opening in the top of the tank, through which the contents are removed by pumping or bailing. The second type has, in addition to a clean-out opening, a drain valve at the bottom, which is operated by a handle extending to a clean-out opening, so that gravity drainage of the tank is possible. The third type is self-draining; as the excreta are added an equal volume of liquid is spilled out the overflow. The solid matter must be removed manually or through the sludge drain. The last-mentioned type requires frequent addition of chemicals, and the others are recharged after each emptying. The presence of odor is an indication of insufficient chemical or of the need for emptying and recharging. The same precautions apply to selecting an area for disposing of the tank wastes as to disposing of the materials removed from cesspools.[11] Since the contents of chemical closets are caustic, they may kill vegetation with which they come in contact. [11] For disposal methods in tight soils, see p. 16.