The method here is to turn the flusher on first to add more water to help the dump flow better. Once empty, close the dump valve for a couple minutes then open again. When empty close the dump valve & continue to let the flusher run letting in a few gallons to slosh around on the way to the next destination.
This method takes a bit of time. We are late departers so we are not the ones holding up others with our time consuming dump ritual. If in a line we don't bother with the flush at all. It is dump & go. Just a few minutes from wheels stop to wheels go.