The "kits" you can buy use phosphoric acid as a cleaner. I use muriatic acid because it's quicker, easier to find and cheaper. It's a lot more dangerous than phosphoric, to you and the environment. Wear protection when using it and kill it with a lot of soda water before dumping it.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.