I’m renting a house with three bathrooms. Two of the three toilets, on separate occasions, spontaneously cracked and leaked water. Both happened between 5am and 6am-ish. I was awake for one and heard it, and woke up shortly after the other one happened and found my kitchen flooded. The cracks in the two toilet water tanks were identical. Given the comments about the water temp and lobby temps, I’m guessing that hour and temperature changes could be linked.

I was able to get the owner of the house to see the wisdom of replacing the third toilet water tank.