How do you clean it? I'm no expert, but I'd turn off the water to the toilet then flush it till it's empty, then hit it with some mould spray. I'd look at the water tank too (which should now be empty) and give that a clean too. Read the instructions on the sprays cos you're meant to leave them for 5-10mins to do their work before you wash them off. Then turn your tap back on and see how you go.