My female corn ALWAYS cr*ps in the tank as soon as I put her back in after cleaning it - I'm not kidding max 20 minutes later I watch her do it.
One day she did 5 in a row before I finally broke down and left it in there as I was running late for an appointment and I swear she knew this was her day to win.
I actually started to wonder if they scent their territory in the wild or something.