Quick Answer:
If water appears at the sink area only when the dishwasher runs, the most common causes are a loose dishwasher drain connection, an air gap or disposal issue, or a backflow/venting problem. Start with simple visual checks under the sink, run a few targeted tests while watching connections, and avoid forcing parts. Many issues can be fixed with a hose clamp or a tightened slip nut; others need a plumber.
Why This Happens
When the dishwasher drains it pushes water through the sink drain system. If any connection is loose, worn, or blocked the draining water can find a path out instead of flowing to the sewer. Common patterns are:
- Loose hose clamp or cracked discharge hose where the dishwasher meets the garbage disposal or sink tailpiece.
- A clogged or partially blocked drain that raises pressure during the fast drain cycle and forces leaks at weak fittings.
- An air gap, knockout plug, or disposal inlet that leaks when water surges into it.
- Venting issues that cause gurgling or pressure changes, making joints move and leak.
Step-by-Step What to Do
1. Prepare and protect the area
- Put a shallow tray or towels under the sink to catch water.
- Turn off the dishwasher power at the appliance or breaker if you’ll be reaching close to electrical parts.
- Have a flashlight and a small mirror or phone camera to see tight spots.
2. Run a targeted dishwasher-only test
- With the sink dry, run the dishwasher on a drain-only or normal cycle while staying at the sink to observe under the cabinet.
- Watch for where water first appears: a drip at a hose clamp, a spray from a cracked hose, or a wet area on the disposal or tailpiece.
- If you cannot see the leak, feel pipes and joints periodically with a protected hand to find moisture.
3. Check the drain hose and connections
- Inspect the dishwasher drain hose where it connects to the disposal or sink tailpiece. Look for loose clamps, splits, or kinks.
- Tighten existing hose clamps (finger tight then a small additional turn with a screwdriver). Replace cracked hoses or clamps if needed.
- If the hose connects to an air gap, inspect the air gap at the sink rim for splash or leaks.
4. Inspect the garbage disposal and tailpiece
- Look at the disposal knockout plug area and the inlet where the dishwasher hose attaches. The connection should be secure and free of corrosion.
- Check the slip nut on the sink tailpiece and the P-trap for loose joints that only leak under flow pressure.
- If the trap feels loose, consult the guide titled Kitchen Sink Trap Keeps Twisting Loose for common fixes before replacing parts.
5. Test venting and observe behavior
- Listen while the dishwasher drains. Any gurgling, bubbling, or noise can mean venting or blockage issues.
- Vibration or strange noise in the drain line may point to pressure or vent problems; if you notice pipe vibration, see the note on Kitchen Sink Pipes Rattle When Tap Opens.
- Slow draining when the dishwasher runs suggests a partial clog downstream; address clogs before tightening fittings.
6. Small repairs to try
- Tighten loose hose clamps and slip nuts—do not overtighten metal slip nuts; snug them and check for leaks.
- Replace cracked or soft sections of dishwasher drain hose; use the same inside-diameter hose and secure with a new clamp.
- Clear minor clogs with a hand snake or by removing the trap and cleaning it manually (see safety notes first).
7. Confirm the fix
- Dry the area, run the dishwasher through a full drain cycle, and watch for any moisture.
- If the leak stops, leave a note in the cabinet with the change you made and the date.
- If the leak continues or you can’t find the source, stop and consider calling a pro (see next section).
What Not to Do
- Do not force fittings or overtighten plastic parts — this can crack connectors and make leaks worse.
- Do not use caustic drain chemicals near dishwasher connections, disposals, or rubber hoses — they can damage parts and are unsafe near electrical components.
- Do not ignore early warning signs such as small drips, damp cabinet bottoms, or fresh stains — small leaks become bigger and damage cabinetry quickly.
When to Call a Professional
- Water continues to leak after replacing hoses or tightening connections.
- There is water pooling under cabinetry, damage to wood, or mold growth.
- Leaks involve the garbage disposal’s internal seals or the dishwasher’s internal pump area.
- Venting issues or repeated clogs that you can’t clear safely.
- Any sign of electrical contact with water or a burning smell — stop and call a plumber or electrician.
Safety Notes
- Turn off power to the dishwasher and garbage disposal at the breaker before working on electrical connections or reaching inside the disposal.
- Shut off the water supply if you will disconnect hoses or remove the trap.
- Wear gloves and eye protection when working under the sink; small metal shavings, dirty water, and sharp edges are common hazards.
- Avoid chemical drain cleaners in this area; use a mechanical method (hand snake) or call a pro for stubborn clogs.
Common Homeowner Questions
- Why does the leak show only during the dishwasher drain? The dishwasher forces water into the drain quickly; any weak joint or blocked section will leak under that surge but not during normal sink flow.
- Can I just tighten everything myself? You can tighten clamps and slip nuts carefully, but don’t overtighten plastic parts and stop if you’re unsure.
- Will a clogged drain cause leaks? Yes — partial clogs raise pressure during fast drains and can push water out at the weakest connection.