This system needs to be carefully manufactured and tested to withstand the pressures involved. Hydraulic hose is a popular choice. You can get CO2 bottles as either gas draw or liquid draw - we would want liquid draw. Quick release connector is at right-hand end of hose. Hose is 6mm i.d. and can take 210bar.
Outer sheath is pinpricked to avoid ballooning if any air seeps out.
Quick release, self-sealing connectors should make filling nice and easy. Hose, connectors and assembly cost about 80. T-piece connecter dismantled showing 'olive' that is compressed round adapter when nut is tightened.