I don't prewash but when there are dirty dishes in the dishwasher it is turned on. Maybe just half a rack full. My dishwasher may run three times in one day The cost of running a not full dishwasher is cheaper in the long run then prewashing or dealing with bugs or exterminators or dishes that sit all day dirty growing bacteria. Why have a dishwasher if you feel guilty about turning it on when there are dirty dishes in it but the thing isn't full? Never understood that reasoning at all.