Quick Answer:
If your kitchen sink holds water briefly and then suddenly drains with a loud whoosh, it usually means water is being released quickly past a partial blockage, a draining appliance is backflowing, or the drain venting is failing and creating a siphon. Run a few focused checks under the sink and on connected appliances before deciding on repairs.
Why This Happens
There are three common causes that create the “fills then whooshes empty” symptom:
- Partial clog or pocketed debris downstream from the trap that traps water until air pressure or a surge forces it through.
- Backflow from a connected appliance (most commonly a dishwasher or garbage disposal) that lets water flow into the sink and then suddenly drain away when its valves or pump run.
- Poor venting — a blocked roof vent or a failed air-admittance valve can let a drain form a siphon so water rushes out when airflow changes.
When you investigate, check both the drain parts under the sink and any connected appliances. For more targeted problems related to heat and trap behavior, consider the article titled Kitchen Sink Drains Fine Until You Use Hot Water, and if the timing matches appliance cycles, also see Kitchen Sink Leaks Only When Dishwasher Is On for appliance-specific checks.
Step-by-Step What to Do
1. Reproduce the problem safely and observe
Run the faucet at the flow and temperature that caused the issue. Watch and listen: does the sink pause, gurgle, or make a vacuum-like sound just before the whoosh? Note whether the garbage disposal or dishwasher is running at the same time.
2. Check connected appliances
- Dishwasher: Inspect the drain hose for a proper high loop or air gap. If the problem happens during or after a dishwasher cycle, the pump or check valve may be allowing sudden flow into the sink.
- Garbage disposal: Run it briefly. A disposal with a partial blockage can hold water and then release it quickly. Also listen for unusual motor sounds that suggest mechanical failure.
3. Inspect and clear the sink stopper and tailpiece
Remove the pop-up stopper or basket strainer and clean debris from the tailpiece opening. Sometimes hair, grease, or food packs around the stopper and forms a pocket that holds water until it breaks free.
4. Remove and check the P-trap
Place a bucket under the trap, loosen the slip nuts, and inspect for clogs or collapsed sections. Clean the trap and run water directly through the trap into a bucket to confirm flow. If the trap is clear but the problem remains, the blockage is farther downstream.
5. Test drain line downstream
Use a hand auger (plumber’s snake) to check the section of drain beyond the trap. Work slowly and don’t force the snake; if you hit resistance and can’t clear it with gentle rotation, stop and consider a professional. After snaking, run the faucet to test.
6. Check venting behavior
- Listen for gurgling in other fixtures when the sink drains — that suggests a venting issue.
- If you have an air admittance valve (AAV) under the sink, listen for a click as water drains. A failing AAV can cause vacuum conditions and sudden whooshes.
- Do not climb onto the roof to inspect the vent unless you are experienced and have proper safety gear; call a pro if you suspect a blocked roof vent.
7. Run a controlled appliance test
With the sink clear, run a short dishwasher cycle or manually run the disposal while watching the drain. Note if the sink level changes when the appliance starts or stops. This helps isolate appliance-caused backflow.
8. Final checks and retest
After cleaning and testing, run the sink multiple times at different temperatures and flows. If the whoosh is gone, monitor the sink for a few days. If it returns, document exact conditions (what was running, water temperature, appliance use) for the technician.
What Not to Do
- Avoid forcing fittings — don’t use excessive force on plastic slip nuts or drain sections; you can crack parts and create new leaks.
- Do not use caustic drain chemicals — they can damage pipes, traps, and finishes and are dangerous to handle. They also interfere with later mechanical cleaning.
- Don’t ignore early warning signs — gurgling, slow draining, and intermittent whooshing are easier and cheaper to fix when addressed early.
When to Call a Professional
Call a plumber if any of the following apply:
- You can’t clear the blockage with a hand auger or the trap removal reveals no downstream clog.
- The problem is clearly tied to roof venting or a rooftop blockage (avoid climbing the roof yourself).
- Appliance backflow continues after you checked hoses, high loops, and air gaps, or the garbage disposal shows electrical or mechanical faults.
- There are repeated backups, foul sewage smells, or water damage signs nearby.
Safety Notes
- Turn off power to the garbage disposal and dishwasher before working on or near them.
- Always place a bucket under the trap to catch water; wear gloves and eye protection when disconnecting plumbing.
- Do not mix drain-cleaning chemicals with manual snaking — leftover chemicals can splash and cause burns or toxic fumes.
- If you need roof access to check vents, hire a professional if you are not trained in safe ladder and roof work.
Common Homeowner Questions
- Why does it sometimes gurgle before draining? A gurgle usually means air is being pulled through a trap or vent while the drain is emptying — often a venting or partial clog issue.
- Could the dishwasher be causing it? Yes. If the timing lines up, dishwasher drain hoses, failed check valves, or missing high loops can let water into the sink and then release it suddenly.
- Is this an emergency? Not usually immediate, but address it quickly to avoid a full blockage or sanitary sewer backup.