We see this quite a bit on home inspection and most home owners think its normal to have draining into there sink when the dishwasher drains. Well its not when water is leaking into your sink from the gap it means that something is clogged. Here are some real simple tips:

• Be sure the kitchen sink drain is not clogged.
• Check the drain hose where it connects below the sink for blockage or a kink in the hose.
• Check the air gap It could be clogged.
Over time, food can clog an air gap, preventing water from flowing. Alternatively, when a new garbage disposal is installed, the installer forgets to remove a knockout plug from the input to which the water line is attached. Either of these situations is quite easy to fix.
With a wet/dry vac, place the hose over the air gap, turn it on, and wait forty seconds to a minute. By that point, anything in the air gap should be sucked out. In some cases you will have to remove and clear out your drain hose.