Dumping the grey after the black is all you'd ever need. If you do this routine and then look inside the hose you'll see it's perfectly clean. You would never sanitize it thoroughly anyway and for what reason?
Also, PLEASE, if you're at a full-hookup site, don't hold your sewer hose under the fresh water faucet to try to clean it. We've seen this disgusting practice too often - not only touching the faucet that others will get their drinking water from but also making a mess on the ground by trying to clean it out after disconnecting it from the RV. Both ends of the sewer hose should always be attached to both the RV and the sewer. Then put it away.
If you feel a need to clean it more, do so at the dump station with the dump station hose - but, since just reading the long post on people taking too long at the dump station by trying to clean their hose and tanks, make it very quick if someone is behind you at the dump station. The dump station is really only for dumping and maybe time to dump a couple buckets of water down the toilet to flush it a little better but not for prolonged filling the tank, dumping, filling the tank, dumping, etc.