It is very difficult to dock 2 grounded crafts especially ones that have little to no translation control (possible using pistons, but tedious) such as rovers, so refuelling is difficult.
This would be a new part, and would work similar to the tether in some functions. An astronaut would approach the pump, free the hose, then carry it towards another craft, and attach it to any part that can contain fuel (even empty nose cones), anywhere on the tank (no need for a receiver-part, so existing crafts can be refuelled). The pump would then be switched on, and then fuel would transfer from one of the crafts to the other (depending on if the pump is set to give fuel, or to take it). The player would use scroll-wheel to increase/decrease the free-length of the hose, and for simplicity's sake, the hose would be linear and straight. The limit of the total length of the hose would depend on the size, adjustable in the VAB.
The hose would create a weak link between the 2 crafts and would detach when the relative velocity between the 2 crafts exceeds a certain limit (for example, 10m/s) AND the length of the free-hose is reached. If the hose detached whilst the pump is still active, fuel would drain out.
Maybe there could be an attachable docking port to the hose, so drones could pick up the hose and refuel without need for an astronaut (the free-hose limit would be controlled in third person using the tether slider (renamed to hose slider)