Thanks to TrueBlue for the macerator idea. I've been doing research to determine if the pump will prevent backflow into the head. I have not been able to find a schematic of a pump, but I did find the following on one manufactures site.
Macerator Pumps are designed to empty your holding tanks when fitted onto the plumbing in both recreational vehicles and boats. The function of the pump is to suction the solids and liquids from the lines connected to the holding tanks and grind the effluent with the rotating cutter head down to a small particle size for simple discharge of the waste. Eliminating gravity as a method to empty the tanks allows the user to lift the waste to a convenient receptacle either above or below the pump elevation
This is the approach we will probably take since we have multiple places to install a larger tank at a higher elevation. In addition to the pump, I plan to install a check valve @ the pumps discharge point.
Thanks for the suggestions from everyone!!