I moved into a house about a month ago. It has one of those overflow valves mounted on the counter by the sink. Today, while running the dishwasher, water poured out of the valve. The deal is, it runs not only in the sink, but also the other direction onto the counter and onto the floor! What is the deal with this thing? It has never run before today, my garbage disposal is clear, the water runs down the sink fine. What can I do to prevent this from happening? I can't have water all over my counter every time I use my dishwasher! Please help!

The washer air gap connects to your disposer or the sink drain above the trap and there may be some clogging in that area. It could also be some slight blochage in the hose from the gap to the disposer. You need to do some detective work to see which is the cause. Are you the owner or tenant? Some plumbers advise removing the air gap and replacing with a high loop under the sink, may not be code in your area but it works.

Ballengerb1 answered your question. I would like to add that from my experience it is one of the four things that causes Air Gap to overflow:

1. Food particles inside 7/8" discharge hose ( this hose connects AirGap and Garbage Disposer )
2. Installer forgot to remove plug from GD
3. Too much food left inside GD plugging the DW inlet
4. Kink in the 7/8" discharge hose

Great points, skip #2 since you have used this dishwasher for a month. Concentrate on 4,3 and then 1. 4 and 3 are very easy to check.

All excellent advice. Her's a little more.
. In the top of an air gap is an insert with two holes. Inside the air gap are two divisions. One division connects to the inflow side of the air gap (from the dishwasher) and the other connects to the outflow side (to the disposal). If the top insert is put in wrong, water will flow from it when the dishwasher empties. For correct operation of the air gap both holes in the insert need to be positioned over the outflow division of the air gap.


In case you ever want to do away with that pesky counter top air gap and install a high loop Air gap.(see image) I'll be more then happy to help.
Note: In all the hundreds of high loop air gaps that my company's installed we have yet to get our first complaint or service call. This holds true in the high loops that we have advised installing on The Plumbing Page right here.
Regards, Tom