Park the truck next to the cistern. Connect a length of hose to the pump supply, drop the hose into the cistern. The pump will move water until it loses suction pressure.
Is the hose to be dropped into the cistern different from the other hoses? I would expect it to be reinforced, such that it wouldn't collapse from air pressure. Hoses downstream from a high pressure pump wouldn't need such reinforcement. However, it's different upstream from such pumps.
