What is a dishwasher high loop? Above you can see the high loop in the photo on the right. In the left photo, there is no high loop. The line in both photos is the drain line from the dishwasher. It typically connects to the sink plumbing above the trap or at the garbage disposal. The purpose of the high loop is to create an air gap between the sink drain and the dishwasher. This will help prevent sink water from flowing into the dishwasher. This important air gap is commonly missing from DIY installs. In older homes, you may see an air gap device next to your faucet that basically serves the same purpose. A missing dishwasher high loop may be an item you find on your home inspection report.