Two odd spots have recently (i.e. in last 1-2 months) appeared at bottom of my most used toilet bowl:

Odd Spots Appeared in Toilet Bowl

They are located symmetrically in what I'll call the two corners at bottom of bowl. I just cleaned/scrubbed toilet and then took above pic. They are rough to the feel, and - I think - may feel a little pitted or as indents as opposed to surface build up.

This is not anything grungy or nasty as it would not soak or scrub away after reasonable effort. I realize I can dump some bleach or other bacteria killer in, but I don't want to mask the problem as opposed to understand and solve it. My main worry is if this is indicative of a bowl failure, i.e. something is wearing/rusting/eating away at those two points.

Also maybe worth noting: my city-supplied water is not at all hard; I have a second, much less used/flushed toilet of exact same model installed at same time as the problem toilet when house was built (~25 years ago) that does not have this issue.

  • This is the lowest point in the toilet, and it could even be a manufacturing defect, so material is likely to settle there and may not scrub out easily. What's your toilet made of? It's likely not the toilet itself rusting out. You might have rust in your water supply, or it could literally be stubborn waste. I would try to drain the toilet or else don gloves and go at that with a plastic knife (non-scraping) to see if its in fact a manufacturing defect. If it is, the toilet may be replaced- a toilet that doesn't reasonably self-clean with a flush is too unsantiary.
    – AdamO
    Commented Aug 17, 2023 at 16:47
  • @AdamO: Standard "builder grade" toilet made of "ceramic" material with "typical" white glazing. Definitely not rust in water supply as our city water is pretty "soft". Also almost certainly not "stubborn" waste. Also unlikely to be a "manufacturing defect" as this is a ~25-year-old toilet and other identical toilet does not exhibit anything close to this.
    – AA040371
    Commented Aug 17, 2023 at 17:50
  • 1
    Rust in lines would be more an issue of household galvanized steel pipes, not likely if plumbing has been redone in <50 years. But anyway, sounds like you are thinking it through more than I can offer. Also city water supplies occassionally change without notice, case in point: Flint Michigan.
    – AdamO
    Commented Aug 17, 2023 at 18:27
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    That's what happens to sections of unglazed porcelain. Stick your hand in the other one; does it feel a little pitted? Doubt it. Or at least it's not as bad? ... It's from manufacturing. Bleach, yes. Or prob anything that comes in the funny bottle for spraying under the lip.
    – Mazura
    Commented Aug 18, 2023 at 2:46

1 Answer 1


Appears to be typical "external kidney stones" - minerals deposited from urine. Both the roughness and failure to scrub away are diagnostic.

Acids will remove them, generally, though patience and scrubbing (with the acid in there, carefully) may both be required. Prevention is usually a matter of flushing after every use, rather than "conserving water" by not always flushing when only liquids have been deposited.

  • 3
    If it's yellow, let it mellow; if it's brown, flush it down!
    – matt.
    Commented Aug 17, 2023 at 16:41
  • That doesn't add up for me. Why would the spots feel recessed?
    – AdamO
    Commented Aug 17, 2023 at 16:42
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    Either that particular part of the toilet bowl is slightly recessed, and favorable for crud to build in; or you have the much less likely (and would not take 25 years to appear) case of the glaze being missing just there.
    – Ecnerwal
    Commented Aug 17, 2023 at 16:46
  • @Ecnerwal agree, the "brown" may be rust in the water supply, urine sedimentation, or actual poo.
    – AdamO
    Commented Aug 17, 2023 at 16:49
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    It's true that I follow Bernie Focker's, via @matt 's reply above, flushing policy...that, coupled with incredibly warm temperatures here may explain it. Although the sudden appearance after ~20 years of virtually identical conditions and use is odd. As to whether these are truly pitted or recessed or not, I have to admit my "feelers" aren't what they used to be as I age, and running my tongue over the spots didn't yield much better results. More than likely I'll let some acid cleaner or rust-disolver sit in it for a few hours and hit it again with a blue scrubber and see what that yields.
    – AA040371
    Commented Aug 17, 2023 at 17:42

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