A liquid catheter, in particular a urinary catheter, includes a catheter shaft part (21) with a longitudinal liquid channel extending between a proximal and distal side thereof, and an anchoring body (22). The catheter body is intended to be received fully internally in a body cavity, such as in particular the urine bladder (50), and to drain the bladder from inside via the urethra (51). The catheter body has a length to span a distance between the bladder and a closure point (35) of the sphincter urethrae. An operating member (24,25) is connected durably to the catheter body to enable a user to carry the catheter body transluminally out of the bladder past the closure point. An insertion device for the catheter includes an insertion sleeve which can be carried transluminally as far as the urine bladder and from which the catheter body can be carried into the bladder.