Plumber's Playbook
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The 60-Second
Toilet Diagnostic

Your toilet won't stop running. In under a minute, you'll know exactly which part is failing and what it costs to fix.

Written by a licensed plumber. No upsells, no affiliate links, no tricks.

What's in the checklist

Five questions. One answer. No jargon.

  1. 1Is the water running constantly, or in bursts every few minutes?
  2. 2Lift the tank lid. Is the water level above or below the overflow tube?
  3. 3Touch the flapper at the bottom of the tank. Is it soft and slimy, or firm?
  4. 4Press down on the flapper. Does the running stop?
  5. 5Look at the fill valve on the left. Is water trickling out the top?

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The 60-Second Toilet Diagnosis Checklist · Plumbers Playbook
Free Checklist · For Homeowners 2026 Edition
The 60-Second Diagnostic

Find the problem before you buy a single part.

Three steps. About a minute of listening and looking, plus a ten-minute dye test. By the end you'll know which side of the tank is causing the trouble. Most of these are cheap parts and a 30-minute job, if you know what you're doing.

Total Time
~ 60 seconds of active diagnosis · plus a 10-minute dye-test wait
1
Listen
10 seconds

Stand next to the toilet for ten seconds with everything else quiet. What you hear narrows down which side of the tank to look at.

  • Constant hiss. → Points to the fill valve side.
  • Water trickling into the bowl. → Points to the flapper side.
  • Cycles on for 10 to 20 seconds every few minutes ("phantom flush"). → Usually a slow flapper leak. Confirm with Step 3.
  • High-pitched whine or vibration. → Fill valve seat. Could be a worn seal or mineral buildup.
2
Look
15 seconds

Lift the tank lid straight up and set it on a towel. Porcelain chips easy. Check these four things in order.

  • Water level. Should sit ½ inch below the top of the overflow tube. Higher than that, the fill valve isn't shutting off where it should.
  • Water flowing into the overflow tube. → Fill valve side, not flapper.
  • Flapper sitting flat on the seat? If it looks warped, mineral-crusted, or cocked sideways, that's worth a closer look.
  • Chain slack. About ½ inch of slack is the target. Too tight and it holds the flapper open. Too loose and it won't lift. Too long and it gets pinched under the flapper.
3
Dye Test
30 sec + 10 min wait

This is the definitive flapper test. Do it even if Steps 1 and 2 looked fine. Silent flapper leaks are the most commonly missed problem.

  1. Drop 5 to 10 drops of food coloring into the tank, not the bowl. Dark color works best. Blue or red.
  2. Do not flush. Wait 10 minutes.
  3. Check the bowl.
Results
Bowl clear
Flapper is sealing fine. The problem is upstream. Fill valve, float, or overflow height.
Faintly tinted
Slow flapper leak. The flapper is the likely culprit.
Clearly colored
Active flapper leak. The flapper is the culprit.
Same color as the tank
Severe flapper leak. Don't wait on this one.
You Found The Problem. Now What?
The fix is in the guide.

This checklist gets you to the right part. The full guide walks you through the repair with photos, exact part numbers, and the gotchas plumbers know that homeowners don't. Grab it for $19 pre-launch at plumbersplaybook.com.

© Plumbers Playbook 2026
plumbersplaybook.com @plumbersplaybook
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Why this is free

Most running toilets get fixed with a $5 part and 10 minutes of work. If I can save you a $200 service call, you'll trust me when I tell you the truth about your next repair.

That's the whole pitch. No newsletter spam, no funnel tricks, no "limited time" pressure. Drop your email, get the checklist, fix your toilet.

A licensed plumber. 15 years in the trade.