.3). Precast cement culvert sections make excellent risers. This step can save a lot of prospecting when the tank requires service. Operation and Maintenance Septic tanks can function very well with a minimum of care. Small amounts of standard household cleansers, drain cleaners, deter- gents, etc., will be diluted in the tank and will cause no damage. Paint thinners, pesticides, some dyes, disinfectants, and other strong chemicals will cause major upsets in the stomach of your septic tank. Also, relatively undigestible materials such as plastic, rubber, nylon, etc. should not be flushed into the tank. They simply accumulate at the bottom (or float at the liquid surface) and increase the frequency of service necessary. Specific items not to be flushed down the toilet include sanitary napkins, coffee grounds, cooking 50 ONSITE WASTEWATER DISPOSAL Figure 4.3 Risers. fats, bones, wet strength paper towels, disposable diapers, and cig- arette filters. The brine solution which is used to recharge home water softeners can be drained into the septic tank without harm. Although it has been theorized that salt could have a bad effect on the drain field if it is located in soils with a high clay content, no such effect has yet been shown. Pollution of ground water by brine coming from septic tanks has occurred and should be considered before purchasing a water softener. There are many products on the market which are supposed to be added to septic tanks in order to prevent or cure any ills that may befall them. Few, if any, of these products have been shown to be of benefit, and some are downright harmful. Ground water contami- WASTE PROCESS Figure 4.4 Measuring the scum layer. nation has resulted from the addition of organic solvents to septic tanks. Be sure to check the contents of any additive before you buy it to make sure that you won't be pouring a cancer-causing agent into your ground water. The best approach is simply not to use them. The only generally required maintenance is to pump out the septic tank periodical