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There was a project to compare pit emptying equipment in Botswana. This was long before the development of any of the current human powered systems but I ttink that one system that was tried has a potential for further development. This was a system for filling drums with sludge remotely from the main tanker. The trial report can be found at: https://www.ircwash.org/sites/default/files/321.4-85EM-2161.pdf
A development of the remote system is possible where the small tank taken to the latrine site is both filled and emptied using the vacuum pump mounted on a road tanker. This is a standard technique used when desludging oil tanks and the like. The mobile tank is connected to the main tanker by an air hose as well as a sludge hose. The remote tank is filled by a hose connected to the top of the tank and extending into the pit using the vacuum via the air hose from from the tanker which would be parked as close as possible. Then the sludge can be transferred to the road tanker by reversing the air flow in the hose to the remote tank, closing a valve on the suction hase from the pit and opening a valve at the bottom of the remote tank and forcing the sludge through the hose to the main tanker by air pressure. This is not limited by atmospheric pressure and the driving air pressure can be a considerably higher and so the sludge can be transported further or raised higher than using a vacuum. The process would need to be repeated as many times as necessary, but the main advantage would be that the remote tank would be empty both when being taken to the pit and when brought back to the road, but the amount of hose required would be considerable and the vacuum pump would need to be quite powerful to overcome friction in long hoses. For long distances it would be possible to have more than one remote tank, but this would add even more complexity to the system.
While this is not going to be a cheap system and would take quite a bit of development (there were a number of problems with the far simpler system that was trialed in Botswana), but I can see no other alternative to manhandling drums of sludge up and down the slopes. I can only wish you luck if you do decide to pursue this approach.