Roughen the external surface of the pipe / fitting end with the file or sand paper. Apply a thin cote of solvent cement on the roughed surface with a brush. Sprinkle dry sand on the solvent cement and leave it to dry for few minutes. A rough base is ready for good bonding with the cement. Insert the solvent cement based PVC pipe in to the C.I. / A.C. socket & fill the gap with regular Portland cement.