The arrangement has an auxiliary lock for introduction into an introduction lock (101) common with a strand-like body/catheter (105). An attaching part releasably fastens the strand-like body at the auxiliary lock. The introduction lock comprises a lock inner chamber (110) with a retainer channel for a strand-like body and a flushing system (108) for flushing the lock inner chamber. The auxiliary lock comprises another lock inner chamber (111) with another retainer channel for the strand-like body and another flushing system (109) for the latter lock inner chamber.