Our macerator also does not have a bypass but I think I wouldn't use one if it did (2008 Monaco Dynasty). I use the same method of releasing the tank contents as I do with the normal sewer hose. I use the gray water to clean out the hose after the black is flushed first.
The macerator hose is smaller in diameter than a regular sewer hose, the overflow of the gray tank will back up into the black tank (if you left the black tank valve open) and help rinse it out too. It's amazing what can be left in the black tank since there is not a 'whoosh' as you would get with a regular sewer hose.
MM.