We rarely used full hookup sites for the reason you talked about. We've seen sewage/toilet paper spilled and folks putting their hose under the faucet. Sometimes the end of the sewer hose was not even put in the sewer - just left on the ground and then they rinsed under the faucet. Yes, we do mention this to campers if we see it being done and have gotten good replies. Some just don't think about what they're doing.
In 16 years of full-timing we never felt it necessary to rinse the hose - even at dump stations. You're not going to sanitize it whatever you do. We dump the black then at least 3/4 tank of grey and we're good to go.
