Unless you have an odd colored toilet, I would not advise trying to patch it. The bad news is that unless it is fairly new, you will not find a tank that will fit it and/or flush it properly. You will have to replace the entire unit, and if the flooring material is caut around the old one, you will also not find one that is the same shape.: Previously you advised silicone to repair a cracked toilet tank. What kind? Spray, caulk, other? Thanks