Hi @Jaseon I assume your talking about a completely empty tank here... Just make sure it dries up completely (evaporates) and then rinse thoroughly with water (and soak up as much of the water you can) to make sure there is no residues left. You can also use a vinegar solution instead depending on the stains you are trying to remove - lime and scale stains comes off fairly easily with a vinegar solution.Is it safe to use inside to clean the glass before adding water.
I usually use it to clean where im using silicon.