RVs can do all of the transfer in and out of an external tank with gravity. That is what the Camco tank is designed to do.
As others said you will need a pump, probably a macerator pump if you already have on installed with a Y valve to divert its output to the external tank. Then you will need about 20' of waste hose from the pump to the tank. Maybe collapsible RV waste hose could work. And then you need to vent the tank. And finally you will need a remote switch to control the pump so you don't blow up your tank once it gets full.
And then you need to wash down your hose- overboard? when you are finished with it.
I would prefer just to get a little wet occasionally.