bleach is a great way to clean a tank... a 10:1 water to bleach ratio will clean the glass and rid the tank of any possibility of a disease... once you clean it real good, let it air dry for a few days, then fill it up with water and use lots and lots of dechlor to make sure no chlorine is left... then empty it, fill it up, cycle the tank, then add fish... btw since it sounds like youre new to the hobby, check out this link on cycling the tank without fish...
fishless_cycling