Quick Answer:

If the overflow still seems blocked after cleaning the bowl, the restriction is often inside the overflow channel. Try flushing the overflow repeatedly to see if flow improves, then inspect the channel for sludge or deposits. If repeated flushing and a visual inspection don’t clear it, call a plumber.

Why This Happens

Water that runs into the overflow channel can carry soap scum, mineral deposits, skin oils and small solids. Over time those materials stick to the inside surface and form a soft sludge or hard scale. Surface cleaning the bowl removes visible buildup, but the channel itself is narrower and less exposed, so deposits there can restrict flow even when the bowl looks clean.

Step-by-Step What to Do

1. Prepare

• Wear gloves and eye protection. Have a bucket and a towel ready.
• Turn off any connected pumps or devices that could run unexpectedly while you work.

2. Flush the overflow repeatedly

• Use a jug of clean water and pour steady, firm flows into the bowl aimed to push water into the overflow opening. Repeat several times over a few minutes.
• Watch whether the water level drops quickly into the overflow or pools. If the flow improves after a few flushes, the blockage may be loosening.

3. Inspect for sludge or deposits

• Look down the overflow opening with a flashlight. Use a small mirror if needed to see deeper.
• If you see brown or gray soft sludge, or white/green mineral crust, that indicates internal buildup that needs attention.

4. Try gentle mechanical cleaning

• Use a flexible brush or a length of soft nylon cable (not metal) to reach into the channel and dislodge deposits. Work gently to avoid damaging fittings.
• After working the brush, flush again to clear loosened material.

5. Repeat inspection and flushing

• Alternate mechanical brushing with flushing until the flow improves or you see no change.
• If debris removed is dark and slimy, it confirms internal sludge; continued flushing should remove most of it if the channel is reachable.

What Not to Do

• Do not keep repeating the same surface cleaning if the restriction is inside the overflow channel. This wastes time and won’t reach the real problem.
• Do not force rigid metal tools into the channel — you can chip porcelain or bend internal parts.
• Avoid pouring strong chemical drain cleaners into the overflow; they can damage finishes and are often ineffective on sludge inside narrow channels.

When to Call a Professional

• If repeated flushing and gentle mechanical cleaning do not restore normal flow.
• If you can see thick, hardened deposits that won’t budge, or if the overflow is filling with dirty or smelly water — check Overflow fills with dirty water for related causes.
• If the problem began after recent plumbing work, and flushing doesn’t help, consult a plumber — see Overflow problem after repair.
• Also call a professional if multiple drains or fixtures are affected, or if you’re uncomfortable working inside the tank or channel.

Safety Notes

• Wear gloves and eye protection when inspecting and cleaning. Sludge can carry bacteria and unpleasant odors.
• Don’t use metal hooks or long hard objects that could break seals or crack porcelain.
• If you choose a chemical cleaner, read the label carefully and use only products labeled safe for your fixture; when in doubt, avoid chemicals and call a pro.

Common Homeowner Questions

• How long should I try flushing before calling someone?
  Try several cycles of flushing and brushing over 15–30 minutes. If there’s no clear improvement, get help.
• Can I snake the overflow like a drain?
  You can use a soft, flexible brush or nylon cable, but avoid metal drain snakes that can damage the channel.
• Is this an emergency?
  Not usually. It’s a maintenance issue unless the overflow is causing water to back up into the room or affecting other fixtures; then act promptly and call a plumber.