the bunghole usually disposed at the middle of its top end plate thereafter the bunghole is tightly closed with the insert to withdraw the liquid there can be used an integrated outlet tap which is disposed on the side wall of the vessel at the height of the bottom end plate thereof the liquid flows out under the action of internal pressure and gravity until a reduced pressure is reached in the top space of the vessel above the liquid surface therein to adjust this correctly and maintain it in controlled manner the compressed co 2 gas source is activated the compressed co 2 gas source injects co 2 into the top space of the vessel under a pressure that corresponds to the partial pressure of the co 2 dissolved in the liquid or that slightly exceeds this partial pressure thereby steady emptying of the vessel is ensured no air is admitted into the top space of the vessel the co 2 content of the liquid remains constant the insert has slender elongated shape and for the most part is radially symmetric relative to a central axis it is made largely of plastic the plastic materials used for its manufacture have proved effective for years for bunghole closures and outlet taps of relevant vessels the two component plastic injection molding technique can be used for manufacture when the insert is in installed condition closing the bunghole of the vessel it projects with a housing 10 into the vessel at its inside end housing 10 has a chamber 12 for receiving a high pressure co 2 cartridge 14 in a snug fit the head of cartridge 14 at the end face of which it can be pierced is.