An endoscopic probe which advances within a lumen having a central valve unit. The valve unit has a central bore defining a proximal end and a distal end, and at least one valve for controlling the introduction and withdrawal of fluid into the central bore. The probe further includes a sliding tubular sheath movably disposed inside the central valve unit, and a flexible sleeve, impermeable to the fluid and sealingly anchored to the central valve unit on both distal proximal ends. The sleeve is folded over to cover both the inside and outside of the sheath to sealingly envelop the sheath and contain the fluid, together with said valve unit, while allowing sliding of the sheath. A method for providing, assembling and operating the probe is also provided.
