ROFL...actually not inside the toilets, but in the button mechanisms you push to drain the water and in the "level floater" which stops the water when the reservoir is full. Those get cluttered by scale every few months. It also does a great job in my Nespresso coffee machine, and is 1000 times cheaper than their cleaning kit, but similar to better results :-)
...and don't use a gallon! leave some scale for posterity ...