A pipe coupling device is disclosed forsealably securing a cylindrical outlet end of a roof drain insert (20), slidable within a larger diameter roof drain pipe (10), coaxially within the drain pipe. The coupling device comprises a compressible, rubber tubular member (40) which when uncompressed is slidable into the drain pipe (10) and which on compression by axially directed compressive forces expands radially outwardly sufficiently to sealably engage with interiorsurfaces of the drain pipe. The rubber tube (40) is adapted on compression to sealably engage the drain insert (20). Screws (50) which are turned to apply axial compressive forces to the rubber tube (40) lie radially inside of the drain insert (20) and are assessible for activation through the inlet end of the drain insert. The pipe coupling provide a means mechanically to locate the drain insert securely within an existing roof drain.