That Jeannea 54DS probably has a larger holding tank than I have on my Morgan 33-O.I., which is just 27-gallons. Consequently, with once a week pump-outs here in the harbor, and $5 for an additional, unscheduled pump-out, flushing with large quantities of water is out of the question. Unfortunately, like most boats, space for the holding tank is quite limited, and in my case the compartment is completely filled with the tank itself.
I've been told that freshwater flushing seems to help quite a bit, and helps promote the growth of good bacteria that promotes healthy tank conditions. I haven't tested that, however, mainly because freshwater in this part of the world is pretty expensive, and it's loaded with chlorine and other chemicals that will kill the bacteria.