I deflated 400 m³ solar balloons by using an internal central rope, and by freeing the traction rope for the lines of my harness: it was enough to wait 2 or 3 seconds that the wind or the aerostatic thrust made the balloon turn over like a sock, deflating completely without effort.
So I think Gangdong system can work.
Also a parachute valve for a hot air balloon could perhaps work, the wind pressure putting it back in place after deflation by traction. But I prefer the internal central rope.