An adaptor 20 temporarily transforms a valved urinary catheter 2 into one that permits continuous fluid flow by deforming the valve 3. The adaptor 20 includes a tube 22 that sealingly engages into the catheter outlet tube 4 and is provided with an actuator member 24 extending therefrom that engages the catheter valve 3. The actuator member 24 is sized to allow urine to flow therearound and into the tube 22, when the member 24 extends into engagement with the valve to deformably open same. However, the actuator member 24 is of a smaller diameter than the tube 22, and therefore does not greatly deform the valve 3 thereby avoiding damage to the valve 3. The adaptor 20 additionally includes a releasable clip 30, 32 that augments the frictional fit between the outlet tube 4 of the catheter 2 and the adaptor 20. The clip 30, 32 can also be sized to interact with a portion of the catheter 2 or the valve housing 5 to ensure the adaptor 20 is inserted an appropriate distance into the catheter 2.