For cleaning a toilet tank, a spray bottle of Lysol multi-purpose with bleach and a grout brush can work wonders. When I moved into my first apartment, I noticed after a couple of days, tiny black pieces kept coming into the bowl. I opened up the tank and found it was almost black (instead of off white)! Tried the bleach tablets in the tank, but they didn't do much of anything. Lysol with bleach and the grout brush and a bit of work and it was clean!