Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.
Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.
Summary
A dishwasher's drain hose has one difficult job: get used water out of the tub without ever letting sink water or garbage disposer water flow back in. The part that stops that backward flow is either a loop of hose raised high under the counter, or a small air gap fitting mounted on the sink deck next to the faucet. This page shows you how to find that loop or fitting under your kitchen sink, check that it is doing its job, and test for the dirty water that shows up when it is not. It needs a flashlight and a tape measure, and takes about twenty minutes.
What this page will not do is hand you one loop height that fits every dishwasher, because the manufacturers do not agree. Whirlpool's own guidance gives at least 20 inches from the floor; GE Appliances publishes a 32-inch loop when no air gap is used. Both are printed here, with their sources, so you can compare your own installation against a real number instead of a guess — and then check the installation instructions for your specific model, because that document is the one that actually governs it. If you find no loop and no air gap at all, or dirty water in the tub after a normal cycle, this page tells you where to stop and who to call.
Necessary equipment
| Item | Note |
|---|---|
| Flashlight | The space under the sink is a dark space. |
| Tape measure | Use this tool to measure the height of the loop. |
| Pen and paper | Use these to record your measurement and the date. |
| Installation instructions for your dishwasher | Many manufacturers publish these on their own website at no cost. |
Prepare to examine the drain hose
Estimated 6 min to 8 min
- Find the model number and the serial number of the dishwasher.1mReport a problem with step 1, Prepare to examine the drain hose
- The rating plate is usually inside the tub or on the door edge.
- Find the installation instructions for your model of dishwasher.3mReport a problem with step 2, Prepare to examine the drain hose
- Manufacturers often publish these instructions on their own website.
- The instructions give the loop height or the air gap rule for your model.
- Find a flashlight, a tape measure, and paper to record your reading.1mReport a problem with step 3, Prepare to examine the drain hose
- Open the cabinet doors under the kitchen sink.<1mReport a problem with step 4, Prepare to examine the drain hose
REMOVE EACH CLEANING PRODUCT FROM THE CABINET BEFORE YOU PUT YOUR HAND INSIDE.
Contact with cleaning products can irritate your skin.
- Remove each cleaning product from the cabinet.<1mReport a problem with step 5, Prepare to examine the drain hose
Locate the drain hose connection
Estimated 2 min
- Point the flashlight into the cabinet.<1mReport a problem with step 1, Locate the drain hose connection
- Find the drain hose that comes from the dishwasher.<1mReport a problem with step 2, Locate the drain hose connection
- The hose is usually black or gray.
- Follow the hose from the wall or the floor of the cabinet.
- Trace the drain hose to its connection point.<1mReport a problem with step 3, Locate the drain hose connection
- The hose connects to a garbage disposer, to a sink tailpiece, or to an air gap fitting.
- Find an air gap fitting on the sink deck or the countertop.<1mReport a problem with step 4, Locate the drain hose connection
- An air gap fitting is a small cylinder next to the tap.
- A removable cap is often on the air gap fitting.
Examine the loop or the air gap
Estimated 4 min to 5 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
Source: Checking the Drain Loop Height · tier 1 · accessed 2026-08-04
Source: Dishwasher - Drain Hoses · tier 1 · accessed 2026-08-04
DO NOT STRETCH A SHORT DRAIN HOSE TO REACH THE LOOP HEIGHT.
A stretched hose can crack and leak water under the cabinet.
- Find the highest point of the drain hose between the dishwasher and its connection.<1mReport a problem with step 1, Examine the loop or the air gap
- If no air gap fitting is present, measure the height of this point above the floor.<1mReport a problem with step 2, Examine the loop or the air gap
- Hold the tape measure against the floor of the cabinet.
- Read the height at the top of the loop.
- Record the measured height and the date.<1mReport a problem with step 3, Examine the loop or the air gap
- Compare your measured height with the height in the installation instructions for your model.1mReport a problem with step 4, Examine the loop or the air gap
- Manufacturers do not agree on one height for every model.
- The specifications on this page give two published examples.
- Make sure that a screw or a clip holds the loop in place.<1mReport a problem with step 5, Examine the loop or the air gap
- The screw or the clip is usually under the counter or on a cabinet wall.
- A loose loop can sag and lose height over time.
- Examine the full length of the hose for a kink or a sharp bend.<1mReport a problem with step 6, Examine the loop or the air gap
- Make sure that the hose clamp is tight at each connection.<1mReport a problem with step 7, Examine the loop or the air gap
The backflow test
Estimated 2 min to 2 min
- Run one normal wash cycle in the dishwasher.<1mReport a problem with step 1, The backflow test
- A normal wash cycle can run for one hour to three hours.
- The cycle must finish before you continue.
WAIT UNTIL THE DISHWASHER IS COOL BEFORE YOU OPEN THE DOOR.
Steam from a recent cycle can burn your skin.
- Open the dishwasher door after the cycle ends.<1mReport a problem with step 2, The backflow test
- Look at the floor of the tub for dirty water or food debris.<1mReport a problem with step 3, The backflow test
- If there is dirty water in the tub after a normal cycle, do not use the dishwasher again.<1mReport a problem with step 4, The backflow test
- Dirty water in the tub after a cycle is a sign of a problem.
- A failed loop or a failed air gap can cause this problem.
- Dirty water on a dish can make a person ill.
After the check
Estimated 2 min
- If your check does not match the installation instructions, speak to an appliance installer.1mReport a problem with step 1, After the check
- Do not change the drain connection under the sink yourself.
- A qualified installer can correct the loop, the hose, or the air gap.
- Return each cleaning product to the cabinet.<1mReport a problem with step 2, After the check
- Close the cabinet doors.<1mReport a problem with step 3, After the check
Terminology
This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.
- drain hose
- Also called: dishwasher hose, waste hose, drain line, dishwasher drain tube
- high loop
- Also called: dishwasher drain hose loop, hose loop, drain loop, loop in the hose, high drain loop
- air gap fitting
- Also called: air gap dishwasher, dishwasher air gap, backflow preventer, the little chrome cap by the faucet, air gap cylinder
- backflow
- Also called: dirty water back in dishwasher, water siphoning back, wastewater flowing back, water running backward into the dishwasher
- sink tailpiece
- Also called: sink drain pipe, tailpiece fitting, drain pipe under the sink
- garbage disposer
- Also called: garbage disposal, disposer, food waste disposer, waste disposal unit
- drain odor
- Also called: dishwasher smells of drain, dishwasher smells bad, smell from the dishwasher drain
When to use a professional
Speak to an appliance installer if you find no high loop and no air gap fitting under the sink. Do not change the drain connection yourself.
Ask a licensed plumber about the local code for a dishwasher drain. Some local authorities require an air gap fitting and do not accept a loop alone.
Do not use the dishwasher again if dirty water enters the tub during or after a normal cycle. Speak to an appliance installer first.
Speak to an appliance installer if the hose is too short to reach the loop height. Do not stretch a short hose yourself.
Common questions
Why does my dishwasher need a high loop in the drain hose?
A loop or an air gap fitting keeps used water in the sink drain or the garbage disposer from flowing backward into the dishwasher tub. GE Appliances states plainly that without a high drain loop or an air gap, dirty water from the sink can flow into the dishwasher. Gravity and a dip in the hose are what let that happen, and the loop simply removes the low point that dirty water would otherwise travel through. This is a plumbing detail set on the day the dishwasher was installed, and it is easy to check once you know where to look.
What is the difference between a high loop and an air gap?
Both do the same job, stopping wastewater from running back into the dishwasher, and most installations use one or the other rather than both. A high loop is simply the drain hose itself, routed up as high as it will go under the counter before it runs down to the disposer or the sink drain. An air gap is a separate small fitting, usually a chrome or plastic cylinder mounted on the sink deck or the countertop next to the faucet, that creates a physical break between the two hoses inside it. Whirlpool's own guidance is that an air gap should be used if the loop cannot reach its recommended height.
How high does the loop need to be?
There is no single number every dishwasher agrees on, which is exactly why this page does not print one. Whirlpool's product help gives at least 20 inches from the floor as its own guideline. GE Appliances publishes a 32-inch high loop from the floor when an air gap is not used, and in a separate support article tells owners to measure their own hose against the height given in the installation instructions for their specific model rather than relying on one universal figure. Treat both manufacturer numbers as examples of how much the figure varies, and use the instructions for your own dishwasher as the number that actually governs your installation.
Why does my dishwasher smell like the drain?
A failed loop or a clogged air gap is one common cause, because it lets sink-side odors and standing wastewater sit against the dishwasher's own drain path. A loaded food filter inside the dishwasher is another common cause and is a separate check from this one. If the smell appears alongside dirty water standing in the tub after a cycle, treat the drain connection as the more likely cause and follow the test on this page.
Is dirty water in the bottom of the tub after a cycle dangerous?
It is not an emergency, but it is not something to ignore either. Dishwater that has siphoned back from the sink or the disposer can carry food debris and bacteria from the drain, and it can sit on your dishes if you run the dishwasher again without checking the cause. Stop using the dishwasher, check the loop or the air gap against the steps on this page, and speak to an appliance installer if you cannot find the cause yourself.
Does my state require an air gap by law?
Plumbing rules for a dishwasher drain vary by state and even by city, and some jurisdictions require a visible air gap fitting rather than accepting a high loop on its own. This page does not name a specific code, because a code we could not read in full is not one we can cite accurately, and code adoption changes by location. Ask a licensed plumber or your local building department which rule applies where you live.
Related procedures
- How to find and record the model and serial number of every appliance in the house
- Decide why water is standing in the bottom of a dishwasher
- How to remove and clean the filter in a dishwasher
- How to clean the drain filter on a front loading washing machine
- How to connect and unclog a dehumidifier drain hose so it doesn't fill the bucket
- How to unclog a slow or blocked drain in a sink, bathtub or shower
- How do I check if my water heater's pressure relief valve pipe is installed correctly
- How to clean a clogged faucet aerator when the water flow drops or sprays sideways
Sources
Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.
Revision history
Current version 1 · updated 2026-08-04 · next review due 2027-08-04
- v1 · 2026-08-04First draft. Sourced to Whirlpool and GE Appliances product support documentation. Loop height publishes as a recorded disagreement between the two manufacturers (Whirlpool: at least 20 in; GE: 32 in when no air gap is used) rather than a single reconciled number. No step touches the appliance's electrical supply or the fixed building plumbing past the drain hose connection.
Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.
Comments and corrections
Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.
Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.