Toilet gets moldy

I have an upstairs toilet that starts growing what I believe to be mold inside of the bowl.It's black in color. It gets cleaned on the same schedule as the other toilets in the house. Can anyone tell me what it is?
dave
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Flush it more often. Its from non use.

inside
the
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you are ill

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I know. Do you still love me ?

as
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Can we still have sex together ? I won't tell.

mold
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on the toilet?? thats just sick!
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Nah, you disinfect it if first. Hell, try it ! Its cheaper than doing it on a boat and both are over water anyway.

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