"Dishwasher discharges on sink"
Column #831 1/29/2011
On The Level
Q. Our dishwasher is 12 years old and works fine but mostly empties when going through its cycles through the air gap. We have replaced the drain hoses and that seemed to work for a while but then the problem started all over again just not as bad. We do not put any food in the dishwasher. Everything is rinsed prior to putting into the washer. So it is not food that is clogging the hose or forcing the drain water into another direction. If we remove the air gap and do not use it anymore will that be a health or other type of problem? Hopefully, you can provide some direction on how we can solve this very frustrating problem.
A. The sink deck air vent waste water discharging you describe is more common with sinks with garbage disposers but isn't confined to them. It was the code to be there when the dishwasher was manufactured and installed and for health reasons I don’t advise plugging it up.
If you look under the sink you will see a hose coming from the dishwasher that is split by a small Y fitting. One part of the split leads to the drain and the other goes up into the chrome thing which sits on the rear of the sink deck. You’ll hear it described as an air-gap,vacuum breaker or vent. It’s all the same.
When the dishwasher drains, it does so with the aid of an electric pump located in the bottom of the dishwasher. The waste water is under pressure from the pump because the waste water must to be pumped up to the drain line under the sink.
If the hose develops a blockage closer to the sink's waste line than the "Y" fitting, then the water will search for the path of least resistance and follow it. In your case, the water discharges up the vent line, out of the chrome vent and onto the sink edge and counter top. I've seen them spray waste water all over the kitchen like a garden hose.
Most of the time the blockage is not food particles. There is a small screen trap located in the bottom of the dishwasher to prevent anything even as small as a grain of rice from entering the drain hose.
The blockage is from a grease build-up. If you could rinse all the grease off the dishes every time you wouldn't need a dishwasher. And dishwasher detergent doesn't always break all the grease down.
Dishwashing takes place at temperatures above the melting point of most edible fats. Dishwashers even heat their own water to get it hot enough. The intention is to emulsify the grease through heat and detergent action and wash it away. That works pretty well most of the time.
Garbage disposers have a nipple fitting on the side of the disposer to attach the drain hose from the dishwasher. When the dishwasher discharges, you can look down into the sink drain and watch the waste water enter the disposer from this fitting in a nice strong stream.
Most people follow a clean-up sequence where the last thing they do before leaving the kitchen is to hit the dishwasher start button. By the time the washer gets to the first discharge stage, the sink and disposer have cooled down from any hot water that may have been in the sink during washing up.
When the warm discharge water hits the cool body of a garbage disposer on its way into the drainage system, it cools. Some of the fats solidify and adhere to the inside of the hose and metal nipple fitting causing a restriction of flow or even a total blockage. Sort of like cholesterol in an artery. The greater the blockage at the disposer the more the vent will discharge water, alerting us to the problem. Our hearts aren't so lucky.
Since you have replaced the hoses before I can rely on your familiarity with the under sink plumbing and will suggest you pull off the hose at the disposer, clean both the hose end and the nipple to which it attaches and reinstall it. It’s a dirty job and one of the best tools if you don’t have a bottle brush handy is a finger.
Or try taking your largest pot and fill it with water bringing it to a boil on the stove. Dump the whole thing into the sink. If you have a double sink, locate the sink which has the disposer and dishwasher drain and pour the water into that one. That might melt the grease and drain it away. It may take more than one dose of boiling water if the build up is substantial. The danger of this approach, apart from handling boiling water, is very hot water can loosen the plumber’s putty that is normally used to gasket the disposer’s attachment ring to the sink and could cause it to leak.
The last piece of good news is when you replace that dishwasher-- and you are getting close due to its age-- the new models do not require the sink deck vent. Technology advances.
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