American Standard 4083 Tank, anyone?

I woke up this morning with Jerry, used the toilet, and a few minutes later heard the ominous sound of water splashing on the floor.

The root cause of this catastrophe is as of yet unexplained.

Luckily we have a bathroom across the hall (the condo's) which we can use. Unfortunately, the toilet cut-off valve doesn't work completely so I had to hack this up: