This one needs a licensed pro
Likely cause: a worn flush valve seat or overflow tube
If a new flapper still leaks, the seat it closes against, or the overflow tube assembly, may be the problem. On a two-piece toilet that is a plumber's job.
Why this happens
A flapper can only seal against a smooth, intact flush valve seat. Family Handyman says the overflow tube may be incorrectly sized, and that when you just can't find a flapper that seals on a two-piece toilet it is time to call a plumber. Korky notes the flush valve seal itself can be what lets water leak into the bowl.
What to do right now
- Run the dye test once more with the new flapper to confirm the leak is still there.
- Check that the flapper matches the flush valve size, 2 inch or 3 inch.
- Turn off the toilet's supply stop if the running bothers you, and turn it back on to flush.
- Call a plumber about the flush valve and overflow tube.
What to tell the plumber
- A new flapper still leaks and the dye test still shows color.
- Whether it is a one-piece or two-piece toilet.
- The flapper size you tried.
Build the full list: what to tell the plumber.
Start this troubleshooter over
References (every fact above comes from one of these pages)
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