A coupling for connection of a tube comprises a coupling housing which includes a first end into which the tube is inserted, a clamping ring which is positioned in the coupling housing against a first conical surface, a sealing ring which is positioned in the coupling housing, and a return ring which is positioned in the coupling housing between the clamping ring and a second end of the housing adjacent a second conical surface that is tapered opposite to the first conical surface. The return ring is expandable and comprises a central aperture which is smaller than the external diameter of the tube. Accordingly, when the tube is pushed into the coupling housing and forced through the return ring, the return ring will expand and move along the second conical surface.