The present invention provides a novel construction for a catheter that includes backflow prevention in the form of a check valve, which keeps the flow of drained fluid material from reentering the patient. The catheter construction of the present invention provides a standard single or multiple lumen tube assembly that extends rearwardly from the insertion end of the catheter to the contact end wherein on the discharge lumen a one way check valve is provided. It is an important feature of the present invention that the check valve is provided as close to the terminal end of the contact end as possible without interfering with the necessary accessory attachment that is typically made thereto. Further, an interlock mechanism may be provided at the terminal end of the catheter for connecting accessories in a positive locking manner. The combination of the valve and the interlock mechanism provides a notable safety and performance improvement that has been previously unknown in the prior art.