Cyborg Ninja

I know this is a gross question, but I'm used to it. I've noticed that wherever I go, if I use the toilet, I end up with dark reddish-brown, almost black, spots on the toilet forming after some time. I'm fairly certain it's from my urine. It affects the toilet seat that I sit on when I pee, and underneath it. You'd be amazed how much urine gets on the seat underneath it. Has anybody else had this problem? It's fairly easy to get rid of, but it always come back of course. I'm kind of worried this is a sign of another medical problem for me. It didn't start until about a year ago.

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