When the installer replaced the dishwasher, did they mount the drain hose correctly? It needs to go from the pump on the dishwasher, in to the garbage disposal. Somewhere in that journey, it needs to go to a point higher than the garbage disposal to prevent food, debris, and leftover water stench from coming out. The concept is just like the "P-Trap" under a sink, but upside down. Normally, if you look under the kitchen sink, you'll notice what looks like a looped up piece of coat hanger that is up near the bottom of the countertop. The drain line is supposed to be supported by that. Good luck and let me know.