If you are concerned about the round hole in the fitting, pictured on the right, it appears to be manufactured, can you see if it is threaded?
I would suspect it to be some sort of last chance relief, as in, if the pressure switch stuck in the on position and the pump kept running with the tank above it's rated pressure, something would blow out of that hole and keep the tank from relieving itself like a bomb.
If that's not it, try dismantling that.
If the tank or the line are flimsy enough to be damaged from disassembly, while exercising s modicum of care, then they shouldn't be pressurized in the first place (thinned out by corrosion perhaps?).