I rarely dump the black from inside-I like keeping my grey closed but love the convenience of opening the grey from inside at 1am when I decide to throw laundry in after a couple of showers-when camping with ciy water it's really easy to fill the grey tank fast...I know the condition of my hose and connectors-and how positive of a connection I made at the sewer outlet in the ground.
I do like to witness the black flow out through the hose-and then the grey flushing over the black to rinse the hose. Sometimes I think the electric valves are like power windows-we got away without them, don't necessarily need them, but no longer live without! Yes, I just put a new passenger window motor in my X at 245K-will that change my purchase plans next time around-no way! Either way-it's very convenient standing outside and leaning over and flipping a switch.