a replaceable ink reservoir for an inkjet printer includes a bag of flexible plastic film . the film is stretched over a plastic plug formed as a thick disc , and an annular ring is pressed over the plug , trapping the film therebetween . the grip achieved by this mode of fastening is secure enough for mechanical strength , and tight enough to seal the ink contained in the bag . no adhesives etc are needed . a needle - pierceable membrane is housed in the plug .