somewhat the same as the earlier answer about routing the hose up in a loop. The water in your dishwasher is probably water coming back from the drain hose when the pump shuts off. Try the loop up as mentioned earlier first -its free. If that dosn't work check at hardware store for a check valve. Its just a "gate" that opens when water is being pumped but closes when pump goes off and prevents water draing back into machine.
GS