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I have no idea what this is called, so I apologize for the vague title. If someone knows what it is, feel free to edit it.

When I turned on my dishwasher (just moved in), water started spewing from this thing. When I removed the cap, I found that it was really dirty and moldy. I'm guessing the previous owners never used the dish washer. I have two questions:

  1. How do I keep water from getting into the silver cap and what is this thing for? There's an opening that allows water to get in when, for instance, I do the dishes.
  2. Is there a valve that needs to be turned off to keep water from spewing out when I use the dishwasher?

sink

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1 Answer 1

Dishwasher drain airgap.

It's placed above maximum sink full water level to prevent siphoning grey-water from the sink into the dishwasher if the P-trap ever gets plugged and you try to empty a full sink.

If water is spewing or leaking from the overflow slots in the cover, either the outflow from the airgap into the sink drain has become clogged (especially if it is set up to discharge into the waste disposal unit, food crud buildup, bioslime growth) or the unit is defective and needs to be replaced.

Diagram on how the drain airgap functions.

Dishwasher Airgap Diagram

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It's pretty likely that there is a clog in the part of the tube that goes to the sink drain. Pull that hose off, and make sure that that it isn't clogged, and that the pipe that feeds into the drain or disposal isn't clogged. I once had a piece of carrot from the disposal clog mine. –  Eric Gunnerson May 5 '13 at 2:49
    
I also had a carrot wedge right where the tube connection empties into the disposal! Carrots make great tubing plugs. If the disposal is fairly new and the dishwasher was never used, the installer may have failed to remove the knockout plug that covers this opening in new units in case there is no dishwasher connection. The installation instructions clearly say to remove this, but who reads instructions? –  bcworkz May 5 '13 at 17:42
    
Oh, that little section on the paper that shows a screwdriver and a hammer? Real Men don't need no manual! And I can see carrot chunks being shoved with enough force to do the ol' "potato up the exhaust pipe" trick. –  Fiasco Labs May 5 '13 at 18:09

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