This is really not a new topic, just a fairly old one revisited ...
I was looking for a solution to quickly drain my fresh water tank for sanitizing and found the solution in the archives under this subject title.
"Robert" on this forum and owner of a '96 U320 suggested an easily overlooked simple suggestion which is to open the outside water faucet in the sanitation bay and turning on the water pump. I drained half my tank in about 10 minutes. Thanks Robert! ^.^d
I just wanted to add that one extra thing that I did. I connected a water hose via a "water thief" to the faucet and used the drained water to irrigate a near by garden. Especially in this very hot dry summer, your plants and trees will appreciate it.
Good tip Ron. I'll just add that you can also tip your coach to the drain side to get that last little bit out.
See ya
ken