If I had to guess, I would expect it to be an older American Standard tank. That problem is characteristic of them, but having one crack does not mean any others will also break.: I came home to find my MBR toilet tank had cracked and : water had been running all day attempting to fill the : tank. Major flooding damage thats resulting in all : flooring on one side of the house having to be replaced. : My concern is what can I do to prevent this happening : again in my other bathroom????