That's great Phil, I wish mine was above the waterline so I could get rid of the pump, as the chlorine attacks the plastic pump and float switch, eventually eating through the seals every 4 or 5 years. *I have thought about lifting the main tank up 12 inches, so I could free flow the effluent too. *Some day, we'll see!! *
I'm in and out of the marina enough that we can empty the pump tank fairly regularly and we're close to the marina's office and heads, so no problem with using our heads at the dock and overfilling the tank.
You mentioned flushing the tank with fresh water? *I have never done that, *is that something they recommend? *
*In 1977, I was told by the boat dealer that my tank was full of Redwood bark strips which acts as a filter medium. *Looking through the inspection hatch, I can see there is some sort of stranded fiber in the tank alright, but I'm not so sure it came from a Redwood tree and I'm not about to pull some out to exam it closely. LOL