Abstract: An anchored guide tube centered on an axis and a conduit passing axially through the tube are relatively sealed by a feedthrough fitting having a flexible and shrinkable sleeve having an inner portion secured to an outer surface of the guide tube at an end thereof and a outer portion folded back over the inner portion and forming an annular fold generally at the tube end. A lubricant or the like is provided for facilitating sliding of the outer portion on the inner portion from a storage position folded back over and lying on the inner portion and a use position extending outward past the tube end away from the inner portion.