As an inspector, we sometimes have to recommend installing an anti-syphon loop in your dishwasher drain line. The reason why you need to install this is to prevent any backflow of water between the kitchen sink and dishwasher or visa-versa.
The loop can be accomplished by two methods. One is the flexible drain hose from the dishwasher goes to an antisiphon valve to prevent back siphoning (this looks like a little air inlet valve through the top of the counter about the size of a salt shaker – usually placed close to the sink). The other method and more simpler method is to take the drain line and make it into a big loop. This loop should go up right under the countertop and then back down to the garbage disposal. This loop of the drainline with an upwards loop helps prevent back siphoning.