Wow that's a major loss of air. Definitely not a slow leak. Maybe the air fill jack or bad servo not closing the valve completely under vibration? Nipple on the air tank? At this point I would completly replace the airlines and air fill jack. Sorry can't be more help but it's really shooting in the dark. Sure would be nice if you could run the plane on the ground with the gear up to help isolate the problem. Otherwise it sounds like a belly landing is coming up.