Full Hookup Issues

We have a clear elbow at the drainage cap on the trailer, and when the black water has stopped completely, my wife goes into the Head with 4 plastic jugs, and one at a time, forces them down "whoosh" as fast as she can, and everyone that has witnessed this has marveled at how much had really still been in the black water tank. And, it never fails, when she gets to the fourth container, everything comes out crystal clear. Then we empty the grey water. I am going to also look into how expensive it will be to "flip" the axles. I could certainly use the height and the extra clearance.