I have a clear elbow on the "sewer hose" that connects to the trailer outlet. This has shown that the first black dump does not get it all, even when using the tank sprayer. (Our 5er has one of those)
I have learned to close the black tank valve after the first dump and do a refill with the water from the sprayer (they warn not to leave it on too long--where "too long " is when it overflows the toilet inside I guess) Meanwhile, to save time at the dump station when there are others waiting their turns, now I dump the galley grey while refilling the black.
Close the galley grey and open the black again for the second dump--lots of white paper going by in the clear window (better than watching TV ! :) ) So this proves you need two goes at it. Three goes is not over-doing it if you want to really get it cleared out, as I have noted in the clear elbow "window".
Now you can do the main grey tank while refilling the black for a third go, or just do the grey and undo the sprayer hose and put that away.
Ok, all done except if you did a third go on the black there is no grey water left to clean out the hose, so you do that with the sani- dump's hose provided for clean-ups.
Of course if there is a big line up at the sani-dump you just do one quicky and get out of there. Do a proper job on the black tank when there is no line up.
