When you have the opportunity to hookup to services it’s important not to leave the waste water valve open because all the liquids will drain but the solids won’t. The liquids help the solids break down, without them you just end up with a bunch of solids and no way to move them out of the tank.
A suggestion is to only empty your black tank once every day or two depending on how much you use it. Right after you empty the black tank empty your grey tank because that water will help rinse any leftovers out of the hose.
I hope helps!
Trusty Wrench RV Doctor 