Quick Answer:
If you see water from the dishwasher dumping into the kitchen sink, the most common cause is the drain hose routing or a partial clog. First check that the dishwasher drain hose rises to a secured high loop or goes to an air gap before it joins the sink drain. That routing prevents sink water from running back into the dishwasher and keeps the dishwasher from dumping into the sink when it drains.
Why This Happens
Dishwashers drain by pushing wastewater through a flexible hose into the sink drain or garbage disposal. If the hose is low, kinked, or tied into the drain without a high loop or air gap, sink water or a clogged drain can flow back. A clog in the sink trap, garbage disposal, or drain line can also force dishwasher discharge to back up and spill into the sink basin.
Step-by-Step What to Do
1. Turn off power and stop a running cycle
Cancel the dishwasher cycle and switch off power at the machine or breaker if you need to work near electrical parts. Keep water and electricity separate.
2. Inspect the drain path under the sink
- Open the cabinet and look at where the dishwasher hose meets the sink drain or garbage disposal.
- Check for obvious kinks, loose clamps, or the hose lying low behind the pipes.
3. Confirm the hose has a high loop or air gap
Make sure the hose travels upward to a point near the underside of the countertop (a high loop) or connects to an installed air gap device above the sink before tying into the drain. The hose must stay raised and be secured so it cannot sag back down.
4. Clear the sink drain and garbage disposal
- Run the disposal (if present) with water to clear food debris.
- If the sink drains slowly, clear the P-trap or use a sink plunger. Removing and cleaning the trap often removes the obstruction.
5. Secure hose and test
- Reattach any loose hose clamps. Use a zip tie or clamp to hold the hose in its high position if needed.
- Run a short drain-only cycle to confirm water goes out and does not flow into the sink.
6. If the hose routing is unclear, stop and consider help
If you cannot find a high loop or air gap, or routing is cramped and confusing, it’s reasonable to call a plumber rather than force a fix that could cause leaks or cross-contamination.
What Not to Do
- Do not lower or remove the high loop/air gap to ‘help it drain’—if routing is confusing, a plumber is appropriate.
- Do not stick a household snake or rigid wire into the dishwasher hose opening; this can damage the pump or hose.
- Avoid running the dishwasher repeatedly with visible backups. That can push contaminated water into the dishwasher or cabinets.
When to Call a Professional
- Persistent backups after clearing the trap and running the disposal.
- Signs of a deeper blockage in the home’s drain line (multiple slow drains, gurgling sounds).
- You can’t find or safely secure the hose to a proper high loop or air gap, or the hose or garbage disposal connections are corroded or leaking.
Safety Notes
- Always disconnect power before reaching into or under the dishwasher.
- Turn off the water supply if you’ll be disconnecting hoses or working on the faucet connections.
- Wear gloves and eye protection when dealing with standing wastewater or chemical cleaners.
Common Homeowner Questions
Q: Why is water coming up when the dishwasher drains?
A: Often the sink drain or disposal is partially blocked or the drain hose lacks a secure high loop or air gap, allowing backflow.
Q: What if the Sink fills when dishwasher runs only sometimes?
A: Intermittent filling usually means a partial clog that occasionally causes backflow; clean the trap and disposal and check hose routing.
Q: Could winterizing cause this problem?
A: Yes—if lines or traps were emptied or reconfigured during winterization, the drain path can change. See Sink fills after winterization for related situations.