A tube coupling for connection to a conduit through which a cable may pass includes a coupling body having an open ended throughway to receive an end of the conduit and a tube locking device in the open end of the throughway for locking the conduit in the coupling body. The throughway has a reduced diameter section with an annular step at an end of the section facing towards the open end of the throughway to receive the end of the conduit inserted into the throughway. An annular flexible sealing member is disposed adjacent the step to be forced by an end of a tube inserted into the throughway into the reduced diameter section of the throughway. Compression of the annular flexible seal forces the seal into sealing engagement with a cable extending along the throughway to provide a seal between the coupling body and cable.