How to Install a Dishwasher High Loop: Code and Steps

What Is a Dishwasher High Loop?

A dishwasher high loop is a U-shaped bend in the drain hose that carries water from the dishwasher to the sink drain or a garbage disposal. The hose is routed upward from the dishwasher discharge outlet, reaches a peak, and then descends to the connection point. The peak of the loop must be higher than the water level inside the sink basin to create a physical barrier that prevents wastewater from flowing back into the machine or the fresh water lines. This U shape also allows air to escape, preventing pressure buildup that could force water back.

Most building codes allow either a high loop or a dedicated air gap. The high loop is simpler to install and often works well for built-in dishwashers that have enough space under the countertop. Portable dishwashers typically connect to a faucet and use a different method, but the same principle applies.

Why a High Loop Matters

Without a high loop, the drain hose can act like a siphon. When the dishwasher finishes a cycle and drains, leftover water in the hose can flow backward if there is any negative pressure in the drain line. That can pull dirty water into the dishwasher or, worse, into the potable water supply. A high loop prevents this by keeping the hose elevated so water cannot naturally travel upward against gravity.

When the dishwasher pumps out water, the hose fills and then empties. If the hose dips low, a siphon can form. The high loop breaks that siphon by creating a point that water cannot pass without external force. Plumbing codes such as the Uniform Plumbing Code and the International Residential Code generally recognize a high loop as an acceptable method of backflow prevention for dishwashers. While the exact height requirement can vary by local jurisdiction, the top of the loop should be as high as possible, usually at least as high as the underside of the countertop. Check your local code and the dishwasher installation instructions for specific guidance.

Measuring and Positioning the Loop

Before securing the hose, locate the connection point under the sink. If your dishwasher drains into a garbage disposal, the hose typically attaches to a nipple on the disposal. If it drains directly into the sink drain, there may be a tailpiece with a branch fitting. The height of the loop is measured from the cabinet floor to the top of the curve.

To get enough height, you often need to route the hose upward along the side of the cabinet before bringing it back down. The loop should be as high as you can make it without crimping the hose. A general rule is to aim for the top of the loop to be above the sink overflow opening. That is a common benchmark because it matches the flood rim level. Use a tape measure to confirm you have at least a few inches of clearance above the highest point where water can sit. If your sink has a tall overflow, you might need to adjust the hose path. The key is to have the peak above the highest point where water can reach, not just the sink rim.

Steps to Form a High Loop

Follow these steps to create a secure high loop. Before you begin, unplug the dishwasher and turn off the water supply. You may need to disconnect the drain hose from the connection point to raise it.

Tie-Down and Support Tips

Use a cable tie or a special dishwasher hose clip to hold the loop in place. You can also attach a 2-inch-wide strap around the hose and screw it to the cabinet side. The support point should be at the top of the loop so the hose does not sag over time.

If your cabinet has a thin back panel, you can install a small screw hook to hang the hose. Keep the fasteners away from sharp edges that could chafe the hose. A rubber grommet or a piece of split tubing can protect the hose where it passes through holes.

• Position the tie near the top of the loop to keep the curve secure.
• Leave a small amount of slack so the loop can flex during vibration.
• Do not overtighten the tie, which could compress the hose and reduce flow.
• Use a metal clamp if the hose is rigid to prevent slipping.

After Installation: Test and Inspect

Once the loop is secured and the hose is reconnected, run a normal cycle with no dishes. Watch the area under the sink for leaks at the hose connections. If water backs up into the dishwasher tub, the loop may not be high enough or the drain line is blocked. Also listen for unusual sounds that could indicate a kink.

Finally, confirm that the drain hose is not in contact with any hot surfaces or moving parts under the sink. A correctly installed high loop should work quietly and reliably for years. For more on drain-related issues, see our guide on dishwasher drain pump vs. gravity and drain hose cleaning.

What to pick for your use

Questions

Is a high loop required by code?

Most plumbing codes allow a high loop as an acceptable method of backflow prevention for dishwashers. Some localities may require a physical air gap instead, especially in commercial settings. Always check your local building code.

How high should the loop be?

The general rule is that the top of the loop should be at or above the flood rim of the sink, which is the lowest edge that water can flow over. In practice, that often means as high as possible under the countertop, usually within the top few inches of the cabinet. The loop must also exceed the highest point of the drain line to break any siphon.

Can I use a high loop with a garbage disposal?

Yes, a high loop works with a disposal. Just connect the drain hose to the disposal inlet and ensure the loop rises above the disposal's lowest point.

What if there is not enough vertical space?

If your countertop is very low, you may need to install a dedicated air gap. An air gap is a separate fitting that mounts on the countertop and provides a physical break in the drain line.

How do I keep the loop from sagging?

Use a zip tie or screw hook at the top of the loop and avoid placing heavy objects on the hose. A support strap around the cabinet can help maintain the curve.