Drain valve or vent valve?

I would've suspected they tried to pump fuel or LOX out and a vent/purge valve didn't open. I've done this - on a water tank, not a fuel tank - but the results were exactly the same.

In my ignoble instance, a make-up 200 gallon fiberglass water tank was vented with an open 1" PVC line routed from the top of the tank and terminated 2" off a concrete floor. Over the years, the pipe clamps holding the open line above the floor loosened and allowed the end of the vent line to contact the floor.

When I turned on the output pump to fill the CWS make-up from that water tank, that vent line snucked-up onto the floor so hard the water tank walls buckled in like an empty beer can does when Daddy's done with the beer he's on and needs 'nother one...

My point is they buckled a tank.

And it wern't no water tank.

Any guess as to how serious of trouble are these guys in?