The device (1) consists of a second connection piece (4), which can be welded via its flange (41) onto an aseptically closed tubular bag (2). A first connection piece (33) can be screwed into the second connection piece (4) and is provided at the end with opening means (34). The first connection piece (33) forms the intake piece of a metering pump (3). Securing means (5) hold the metering pump (3) in the correct position relative to the second connection piece (4) before the first use, and further means hold the metering pump (3) in the correct position relative to the second connection piece (4) in the use position.