Any question answered...

The ceramic under the waterline is brown, attacked it with bleach and a good strong brush and it's hardly done anything to it. The previous user didn't keep the best hygiene in work

Often when industrial strenght cleaners don't work a bit of elbow grease does the trick. Scouring pad (and glove if you are one of those Howard Hughes types) and go at it. Depends how long it's been there but doesn't usually take much shifting.