I've learnt to not get to distracted while a tank is filling. I learnt the hard way- ran into the room as water was gushing over the edges straight onto the television and the plugs for the tank!
Same thing goes for emptying - set up 2 siphons at a time by clipping one to a tank. Wasn't watching and sucked up one of my South American Puffers- he started to puff. Stopped the siphon and he is ok.