You ended up being a tank cleaner, how? No idea. you'd clean the inside of tanks in the morning and clean the outside before your shift ended.

while cleaning a tank for the first time. you heard a thump and looked up to see what happened.

A shark human thing was trying to eat the brush from the inside of the tank. It's tail thrashing around. You looked at the thing with fear, it's sharp teeth an large, white tip reef shark tail that was obviously strong enough to smack something really hard.