I've always had good luck with the clamp on chain cleaners that use the 3 wheel brushes. BUT.... I replace the solvent and repeat as needed until it barely becomes coloured from the chain running around in it for a good three to four passes through the cleaning gizmo. Generally this is three times. On an exceptionally dirty and long ignored chain it may be 4 or 5 switches before it's properly clean. If you didn't keep at it until it left the degreaser quite clean then that would explain why there was residual sand still in the chains.

I use a low odour paint thinner as my solvent. I pour it into a setting jar when dirty and once the grit settles and leaves a clear tea like upper area I can decant that solvent off and reuse it over and over again. Only my final change to fresh solvent uses a little dribble of the new stuff from the jug.