eherlihy showed one possible arrangement. But in common with all there is no "overflow" outlet. It's possible you blew the vent fitting off the tank, possibly because the vent may be plugged. You should have a way of telling when the tank is 3/4 full - it's an ABYC regulation. If the vent was plugged and you filled the tank the pressure had to go somewhere. Hopefully you have access to replace the vent fitting but you should get the tank pumped out first. If you don't have access removal of the tank is necessary to repair it. Good luck.
Living aboard in Victoria Harbour