Though it probably varies from model to model, jester and Robin are/could be both correct. I put a Flojet 18550000A in my bus. It is claimed here
that this model will self-prime up to 4 feet above the liquid level in the tank, and the "head capacity table" shows flow rate for up to 25 feet of head (vertical lift). I've installed mine even with the bottom of the tanks and I don't anticipate ever using more than just a few feet of lift to empty the tanks, but it's nice to have the option.
Xylem, which owns the FloJet brand, also owns the Jabsco brand under which several "electric toilet" options are offered. I haven't studied them in any depth, but they appear to include waste and/or supply water pumps that could make a remote black tank feasible.