I used to work at a pet store that had a bunch of tanks, we didnt have a central system so all the tanks were individually filtered. Anyway, I was filling our 90G showtank, walked away for like 2 minutes, I heard some kid say "theres water on the floor" I was like holy S***! sure enough the tank overflowed and there was water everywhere.
In another epic story, we used a 55 gallon trash can for when we drained the tanks, before the idea of running the pump to the bucket we used to push it into the back room to drain it.. yeah well, my manager hit that one little bird seed on the floor and WHOSH! down it goes HOWEVER! Due to ninja like abilities she caught that before it went completely over. Spilling maybe 10 gallons if that. But she has managed to knock over all 55 gallons before. I am lucky I wasnt there for that.