Water from the air gap indicates a restriction after the air gap—commonly the hose to the disposal or sink drain—not a reason to remove the air gap. Run Cancel/Drain and watch when water exits, then have the hose checked for kinks and packed food waste.
What this covers
- Dishwashers · drain plumbing
What it does not cover
Differential
Likely causes of “Dishwasher air gap overflows onto the sink”, and how to tell them apart
- 1
The hose from the air gap to the disposal or sink drain is kinked or blocked
What separates it Water bubbles out of the air-gap cap on the sink while the dishwasher drains, and the drain is slow.
How to confirm Run Cancel/Drain and watch when water exits, then have the hose checked for kinks and packed food waste.
- 2
A disposal knockout plug was never removed
What separates it The problem started after a new disposal was installed and dishwasher drain water cannot enter it.
How to confirm Ask whoever installed the disposal, or have it checked, since the plug sits inside the inlet port.
- 3
The sink drain itself is restricted
What separates it The sink also drains slowly, and water rises when both run together.
How to confirm Run the sink alone and time it; a slow sink points at the household drain, not the dishwasher.
- 4
The air gap cap or body is clogged with debris
What separates it Water sprays or trickles from the cap in small amounts and the cap looks dirty inside.
How to confirm Remove the cap when the machine is off and look inside for buildup.
Before you touch a setting
Record this first — changing settings destroys the evidence
- The exact moment water leaves the air gap: at the start of drain, during the drain pump run or after the cycle ends.
- Whether the sink or disposal is slow when the dishwasher is not running.
- Whether the disposal was installed or replaced shortly before the problem began.
Try in this order
0 of 4 completedObserve before changing anything
ReversibleRun Cancel/Drain and observe exactly when water exits the air-gap cap.
Isolate the failing boundary
ReversibleDisconnect power and have the hose from air gap to disposal checked for kinks, blockage and an unremoved disposal plug.
Apply the narrow correction
ReversibleClean and reconnect the approved drain path while preserving the air gap.
Verify the result and stop at the boundary
ReversibleStop for wastewater backup, leaks under the sink or uncertain plumbing connections.
Stop boundary
When this stops being a self-service repair
- !Stop for wastewater backup, leaks under the sink or drain connections you cannot identify; leave plumbing changes to a qualified plumber.
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Should I remove the air gap to stop it overflowing?+
No. The air gap is a backflow safeguard that some codes require. The overflow is a symptom of a restriction further along the drain line.
What is an air gap?+
A fitting on the sink that prevents dirty water from siphoning back into the dishwasher.
Why does it overflow?+
Usually the drain hose, disposal or sink drain downstream is blocked, so water backs up through the air gap.
Is it safe to remove the air gap?+
No. Local code may require it. Clear the downstream blockage instead.
Why does water spill from the air gap during draining?+
The drain hose or disposal is clogged, so water backs up and escapes through the air gap. Clear the blockage.
Do I need to knock out the disposal plug?+
A new disposal's dishwasher inlet has a plug that must be removed, or the dishwasher cannot drain.
Is a high loop an alternative?+
Many areas allow a high loop in the drain hose instead of an air gap, but local code decides.