View Here : Dishwasher High Loop
The dishwasher high loop drain line is shown in the image. The high loop is shown properly fastened to the underside of the countertop as needed. An air gap is a vent that goes up through the top of the sink or countertop. An air gap is optional, but not needed with a properly installed high loop drain line.
Bosch: The high loop in the drain hose of your dishwasher is to keep water from settling in the hose if it were hanging down any lower or horizontally. This keeps the drain hose dried out and keeps any odors from backing up into the dishwasher.
No high loop. Bosch: The high loop in the drain hose of your dishwasher is to keep water from settling in the hose if it were hanging down any lower or horizontally. This keeps the drain hose dried out and keeps any odors from backing up into the dishwasher.
Dishwasher – air gap – high drain loop. The purpose of a dishwasher high drain loop is to prevent back flow of water. The water can flow back into the dishwasher which will leave water in the bottom of the dishwasher. The high drain loop is also there to prevent improper drainage of water while the dishwasher is running.
Dishwasher High Loop and Air Gap Devices. The easiest way to plumb the dishwasher drain is often into the sink drain piping. A plastic hose about ¾” in diameter runs from the dishwasher to the drain line under the sink. The hose is attached to the garbage disposal or Tee’d into the piping upstream of the trap.
Dirty water entering the dishwasher and not draining could be because there is no air gap or high drain loop installation. Learn more at http://www.geappliances.com.
The purpose of the "high loop" or mechanical "anti siphon device" is to prevent the waste water from the kitchen sink from entering the bottom of the dishwasher when draining the sink basins.
The only time a dishwasher doesn't need that high loop is when there is an air gap — a little fitting that looks like a short piece of pipe with vents at the edge of the sink. If you have neither, you can add the high loop, assuming the drain hose is long enough. If it isn't, replace the hose and add the loop.