[Desert185]

If I have folks waiting behind me I use the black tank flush during the drain cycle to provide a bit more motive flow to the process. When its time to close the black tank drain, I leave the flush running for a couple of minutes while draining the gray tanks. This puts a few gallons of water into the black tank, so I just have to squirt some Dawn into the toilet (after I get out of the way) for the next cycle.

If I'm at a site that has a sewer connection, then I do the flush cycles as needed until I get a relatively clean flow.