The Joys of Home Ownership - Dishwasher Edition

The things you learn as a homeowner. In Kentucky, code requires that an air gap device be installed on the drain line from the dishwasher. Conceptually, I understood that this was a backflow prevention device that kept waste water from flowing back into the dishwasher during the drain cycle. However, I was ignorant of the exact mechanical workings.

Well, the past few weeks, the air gap was overflowing into the sink whenever we ran the dishwasher. Naturally, my wife was concerned about it and wanted the problem fixed. Thanks to the wonders of the internet and various DIY sites and videos on YouTube, I now understand how these things work, and what usually goes wrong with them.

The good news is that the air gap itself is a very simple device, mechanically. There are no moving parts whatsoever.

Dishwasher Air Gap

The dishwasher drain line connects to the nipple at the bottom of the air gap. The water flows up into a reservoir, and then is gravity fed back out through the nipple that sticks out at an angle. That outflow line is a 7/8" inner diameter hose that connects to the garbage disposal (if you have one) or to the plumbing stand pipe under your sink. The number one cause of overflow is constriction in that outflow hose. That constriction can either be a kink in the line or a dip (a u-shape) that drops below the connection point to the plumbing, or it can a build-up of gunk in the line.

In my case, it was a build-up of gunk. The link was a straight shot from my air gap to my disposal with no kinks or dips (it was "downhill all the way"). I removed the hose and upon visual inspection I could only see a pin prick of light through one end. I flushed the hose with water from my outside hose. I didn't bother washing it out with soap or other cleaners. Once it was nice and clear, I hooked it back up to the air gap and the disposal.

I haven't run a load through the dishwasher since I fixed it, but I'm fairly confident my issue has been resolved.

Oh, the number reason for the outflow device to overflow? That would be an incorrect installation of your garbage disposal. There is a nipple on the garbage disposal for your dishwasher drain line. Well, since not everybody has a dishwasher, the inlet hole is covered with a knockout plug. If you don't remove that knockout plug, obviously there's no where for the water to go. I almost made that mistake myself when I replaced our garbage disposal a year ago.

The LORD bless you and keep you; the LORD make his face to shine upon you and be gracious to you; the LORD lift up his countenance upon you and give you peace.
Numbers 6:24-26 (ESV)