The invention relates to a closing unit for a throughflow opening of a container or conduit, the closing unit comprising:a first closing element (4) configured to be mounted or integrally formed on the container or conduit, wherein the first closing element comprises a receiving part provided with a passage and to be arranged in or round the throughflow opening;a second closing element (6) comprising a closing part configured to be received by the receiving part and to be coupled releasably thereto for the purpose of closing or leaving clear the throughflow opening; wherein the releasable coupling between the receiving part and closing part comprises a conical threaded coupling.