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Apologies in advance for posting something so gross, but I'm having the unenviable task of cleaning this disgusting thing but have no idea what the black is. I've not actually seen it, only this picture - so don't quite know what to go armed with product wise. Vinegar/baking soda? Bleach? Coca Cola
I'm aware of black accumulating in toilets at the water line when they're not cleaned regularly, but not all the way up the bowl itself.
For heaven's sake!!! Just spray it with some bleach based product and leave it for a couple of hours or ideally overnight. Not need to over-react over this!!