DEAR MIKE: Whenever I run my dishwasher, water runs out onto the top of the sink. Is the problem my dishwasher or something else? -- Gerald G.
DEAR GERALD: The problem isn't the dishwasher. It is somewhere between the air gap (the thing on top of your sink that is spitting out water) and the disposal.
The air gap makes it so that contaminants from your drain/sewer system (that is, wastewater) can't be siphoned into the clean water system (in this case, your dishwasher).
Under the sink, the air gap has two openings. The inlet is smaller than the outlet, because the outlet relies on gravity to carry the waste away.
The dishwasher's drain hose is connected to the smaller inlet tube, and a rubber hose connects the larger outlet of the air gap to the garbage disposal. Your air gap will only leak when the dishwasher is draining because that is the only time water is passing through it.
To diagnose the problem, start at the disposal and move backwards to the air gap. If you have recently had a new disposal installed, the installer may not have removed the knock-out plug that allows the discharge to pass through. This will cause the discharge to back up and out of the air gap.
To fix this, just unscrew the hose clamp that holds the rubber hose to the disposal and pull off the hose. Then hit the plug out with a screwdriver and a hammer.
Most of the time the problem is with the rubber hose. It gets filled with debris from the dirty dishes (a good reason to rinse the junk from the dishes before you put them in the dishwasher). With the hose removed from the disposal side only, stick a long screwdriver up the hose and pull out some of the gunk. Then get a bucket and point the hose into the bucket.
Run the dishwasher just long enough for it to fill with some water, then drain it. The water should shoot out of the hose (along with a little debris). This should solve your problem.
Take note of how the hose was installed. You don't want any kinks or bends that may reduce the volume of water that flows through it. If the hose has a kink or bend, trim the end of the hose until it fits smoothly. The air gap relies on gravity to evacuate the drain water, so make sure the hose runs downhill.
If the air gap still leaks after all this, it's time to replace it. You will need to unscrew the two hose clamps at the bottom of it and pull off the hoses. The air gap is held to the sink by a plastic collar that screws on from the top of the sink. Simply unscrew this collar and the air gap will pull out from under the sink.
It is a lot easier to attach the hoses to the air gap before you re-attach it to the sink. Push the dishwasher drain hose on the smaller inlet and the disposal hose on the larger outlet. Tighten hose clamps around the end of the hoses until snug. Thread the air gap through the hole in the sink and tighten the collar on top of the sink to hold it in place.