Tuning Kral big max x leaking air

If you shoot it down to below a certain LOW PRESSURE point it's likely to leak all the air out (which can be totally normal for any PCP) and likely be difficult to hand pump from ZERO pressure unless you cock it first or double load 2 pellets to block the transfer port to allow pumping from zero start pressure.

If you have zero air in the gun then I would try to screw the TWO bottles in tighter b4 refilling.