If you are in a hurry muratic acid is very quick. It has nasty fumes so do it outdoors and make sure you have removed the petcock regardless of how you do it. Rinse the whole tank quickly with water followed by with a few tablespoons of baking soda in a quart of water, slosh it around on all surfaces even if you had the acid only in the bottom of the tank. The fumes alone will leave a residue that will cause flash rust unless neutralized. CLR will work to remove light surface corrosion or flash rust and it is not so nasty to work with. Again you have to neutralize it afterward, same with The Works toilet bowl cleaner. Unless your tank is compromised by corrosion I would not use a tank liner. They fail all to often more than likely caused by poor application by folks who cut corners and don't follow instructions to the letter. The idea that you can put a liner over corrosion in a tank is absurd to me. Vinegar or molasses work too if you don't mind the extra time and have the benefit of not being nasty to work with. There is Evaporust and electrolysis too. Take your pick.
