If your sink drains, but water pools for a while before slowly disappearing, you’re dealing with a slow drain. This is a very common issue and usually means buildup is restricting water flow — not that the pipe is completely blocked.
Slow drainage often gets worse over time if it isn’t addressed.
Quick Answer:
A sink drains slowly because debris is partially blocking the drainpipe. This is most often caused by grease, soap residue, hair, or food particles building up inside the P-trap or drain line, restricting water flow.
Why This Happens
Sink drains rely on smooth pipe walls and steady airflow to move water away quickly. When residue builds up, water still drains — just much more slowly.
Common causes include:
- Soap and hair buildup in bathroom sinks
- Grease and food residue in kitchen sinks
- Sludge buildup inside the P-trap
- Minor blockages further down the drain line
- Poor airflow from venting restrictions
A slow drain is different from a sink that won’t drain at all, which usually indicates a complete blockage.
Step-by-Step: How to Fix a Slowly Draining Sink
Step 1: Flush with Hot Water
Run hot water for several minutes.
This can help:
- Melt grease buildup
- Loosen soap residue
- Improve water flow temporarily
If drainage improves only briefly, buildup is still present.
Step 2: Check the Drain Opening
Look into the drain opening for visible debris.
If you see:
- Hair
- Soap scum
- Food residue
Remove anything you can safely reach.
Step 3: Use a Sink Plunger
Use a flat-bottom sink plunger.
- Cover the overflow opening if present
- Add enough water to cover the plunger
- Apply several steady plunges
Plunging can clear partial clogs that cause slow drainage.
Step 4: Clean the P-Trap
Slow drains are often caused by buildup in the P-trap.
- Place a bucket underneath
- Remove the trap carefully
- Clean out debris and residue
- Reinstall and test
This step resolves many slow-drain problems completely.
Step 5: Observe Other Drains
Run water in nearby sinks or fixtures.
If multiple drains are slow, the issue may be further down the line and may overlap with causes behind sink gurgling or drain backups.
What Not to Do
- Don’t ignore slow drainage
- Don’t use chemical drain cleaners repeatedly
- Don’t pour grease down the sink
- Don’t assume slow drains will clear on their own
Slow drains usually worsen without intervention.
When to Call a Professional
Call a plumber if:
- Slow drainage returns quickly after cleaning
- Multiple sinks drain slowly
- You hear gurgling noises
- Water backs up into other fixtures
These signs often indicate deeper drain or vent issues.
Safety Notes
- Avoid splashing dirty drain water
- Wear gloves when cleaning traps
- Tighten fittings gently to prevent leaks
- Test for leaks after reassembly
Common Homeowner Questions
Why does my sink drain slowly but not clog completely?
Partial blockages allow some water through but restrict flow enough to slow drainage.
Can boiling water fix a slow drain?
It can help temporarily, especially with grease, but it won’t remove solid buildup.
Is a slow drain a serious problem?
Not immediately, but it often leads to full clogs if ignored.