I use the same method you do for rinsing the black tank. However, occasionally when I would leave it connected and we would change locations and we changed elevation the water would pressurize in the hoses and drain out of the hoses into under the sink where that siphon break is. We learned to store old towels under there until I figured out what was causing the water to enter there. When the "leak" occurred the 2 or 3 towels were soaked.
Now, when I'm done rinsing the black tank, I disconnect the quick-disconnect end of the blue hose and let the water drain out of all the lines onto the ground. It only takes 15 seconds. Then I just leave the blue hose quick-disconnect end disconnected until it's time to use it again. No more water under the sink with this method.
Pat & Karen
2012 CC Silverback 29RE
2013 Ford F250 Lariat, Crew Cab, Short Bed, Diesel, 4WD
Retired and trying to travel where it's warm.