Cleaning an undermounted sink?

We have a Marble counter with an under-mounted sink in our upstairs bathroo m. There is a small gap where the sink attaches to the countertop and ther e is a reddish stain on the top of the sink that is visible in that gap. I think it was something my daughter was using. It's a mystery.
I tried using a toothbrush and comet but it didn't come off.
I know the marble etches easily but since this is the underside I can use s omething stronger as long as I'm careful not to splash it up on top of the marble.
Are there any other cleaning products you would recommend to try and get so me of that gunk off?
I know as a last resort I can disconnect the sink and pull it out and clean it but would really like to avoid having to do that.
Thanks in advance for any suggestions.
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On Monday, August 15, 2016 at 7:37:32 AM UTC-4, snipped-for-privacy@hotmail.com wrote:

ere is a reddish stain on the top of the sink that is visible in that gap. I think it was something my daughter was using. It's a mystery.

e marble.

I'd try bleach, right out of the bottle. Apply it and let it sit for 15 mins. Works for me on my counter stains.
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On Monday, August 15, 2016 at 8:55:47 AM UTC-4, trader_4 wrote:

My go-to is Oxyclean for my sink stains.
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We have a Marble counter with an under-mounted sink in our upstairs bathroom. There is a small gap where the sink attaches to the countertop and there is a reddish stain on the top of the sink that is visible in that gap.
It sounds to me like one of two things: Rust in the water or fungal growth. For the latter you can try bleach. If that doesn't work then one of those mineral deposit cleaners might do it. I think Dep makes a good one, though I lose track of which product works and which doesn't.
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We have a Marble counter with an under-mounted sink in our upstairs bathroom. There is a small gap where the sink attaches to the countertop and there is a reddish stain on the top of the sink that is visible in that gap. I think it was something my daughter was using. It's a mystery.
I tried using a toothbrush and comet but it didn't come off.
I know the marble etches easily but since this is the underside I can use something stronger as long as I'm careful not to splash it up on top of the marble.
Are there any other cleaning products you would recommend to try and get some of that gunk off?
First of all, it is highly unlikely that the sink is marble; most likely it is faux marble made of polyester resin or china. Does it look like marble or is it china?
I also kind of doubt that your daughter is culpable; about all the gals use that is reddish is lipstick and rouge and she would have to intend to put those there. On the off chance that is what it is, any grease solvent like paint thinner should dissolve it.
Most likely it is rust from iron rich water that has been repeatedly splashed there and then evaporates. If that is the case, rust removers like CLR should work.
If those don't work, you could physically abrade it - marble or faux marble or china - but you'd have to use something more abrasive than Comet...fine, powdered pumice made into a paste would work, so would fine wet or dry paper. If you have to abrade it, the surace gloss will be removed. It could be repolished with a Dremel type tool equipped with a small cloth wheel charfed with a polishing compound. If china, it would be much more difficult to re-polish unless the material used to abrade was quite fine
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On Monday, August 15, 2016 at 11:14:22 AM UTC-4, dadiOH wrote:

I'm pretty sure that he didn't mean to imply that the *sink* was marble. He mentioned marble because he is concerned with damaging the counter top material. In fact, he is not even worried about damaging the underside of the counter, only the top.
"I know the marble etches easily but since this is the underside I can use something stronger as long as I'm careful not to splash it up on top of the marble."
He wants to clean the top of the sink lip, which may mean "cleaning" the underside of the marble counter simply due to it's physical proximity to the sink.
...other good suggestions snipped...
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Yeah, I understood, just covering all bases :)
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On Monday, August 15, 2016 at 1:39:00 PM UTC-4, dadiOH wrote:

Oh sure, throw in another variable. We don't know what the base is made from. ;-)
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On Monday, August 15, 2016 at 11:14:22 AM UTC-4, dadiOH wrote:

She said the counter is marble, not the sink.
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