Thermocure is designed for cleaning engines, largely through driving the car for several hours to allow the heat of the coolant to react with the coolant to remove the rust. I'm sure people try all sorts of things but you're better off using a product that is designed for shower heads & toilets. Repeated exposure to that hot solution is what does it. By the way, if you have really hard water and the toilets have been there for quite awhile you may need to replace them. Our water here is really hard and all our toilets started not flushing well. I replaced one toilet and when I turned it upside down found the minerals had reduced the diameter of the poop tube to just a fraction of new. Had to replace all our toilets to resolve. No quick "pour through" fix would have helped.