If your sink won’t drain at all and water just sits in the basin, it’s a clear sign that something is blocking the flow of water. This can happen suddenly or build up over time, and it’s one of the most common plumbing problems homeowners face.
In most cases, a sink that won’t drain is caused by a blockage close to the sink itself — not a major plumbing failure.
Quick Answer:
A sink won’t drain because water is blocked by a clog in the drainpipe, P-trap, or branch line. This is most often caused by grease, soap residue, hair, food particles, or debris that has built up over time.
Why This Happens
Sink drains are designed to carry water and small debris away quickly. When buildup accumulates inside the pipes, water movement slows and eventually stops.
Common causes include:
- Grease or food waste in kitchen sinks
- Hair and soap buildup in bathroom sinks
- Objects accidentally dropped into the drain
- Residue buildup in the P-trap
- Partial blockages further down the drain line
A sink that won’t drain is different from a sink that drains slowly, which usually means the blockage is smaller or less developed.
Step-by-Step: What to Do When a Sink Won’t Drain
Step 1: Stop Running Water
If the sink isn’t draining, stop using it immediately.
Continuing to run water can:
- Fill the basin completely
- Increase spill or overflow risk
- Make cleanup harder
Let the standing water settle before troubleshooting.
Step 2: Check for Visible Obstructions
Look inside the drain opening with a flashlight.
If you see:
- Food debris
- Hair clumps
- Soap buildup
Remove anything you can reach safely by hand or with a tool.
Step 3: Try a Sink Plunger
Use a standard sink plunger (flat bottom).
- Cover the overflow opening if present
- Add enough water to cover the plunger cup
- Apply several firm plunges
Plunging can clear many clogs located just below the drain opening.
Step 4: Inspect the P-Trap
If plunging doesn’t help, the clog may be in the P-trap under the sink.
- Place a bucket underneath
- Loosen the slip nuts
- Remove and inspect the trap
This is one of the most common clog locations in sinks.
Step 5: Test the Drain
Reassemble the P-trap and run water slowly.
If the sink still won’t drain, the blockage may be further down the drain line.
This often overlaps with issues that cause sink backups or gurgling noises, especially if other fixtures are affected.
What Not to Do
- Don’t keep running water into a non-draining sink
- Don’t rely on chemical drain cleaners
- Don’t force objects down the drain
- Don’t ignore standing water for long periods
Chemical cleaners can damage pipes and often don’t remove the full blockage.
When to Call a Professional
Call a plumber if:
- The sink won’t drain after clearing the P-trap
- Multiple sinks are backing up
- You hear gurgling from nearby drains
- Water backs up into other fixtures
These signs often indicate a blockage deeper in the plumbing system.
Safety Notes
- Turn off the faucet before disassembling plumbing
- Keep a bucket and towels nearby
- Avoid contact with dirty standing water
- Tighten fittings gently to avoid leaks
Common Homeowner Questions
Why won’t my sink drain even though it isn’t clogged at the top?
The blockage is often located in the P-trap or further down the drain line.
Can a sink clog fix itself?
Rarely. Most clogs worsen over time if not addressed.
Is it safe to use drain cleaner?
Chemical cleaners can damage pipes and are not recommended for frequent use.