Assuming both ends of a pipe are submerged in the same body of water, pumping upwards requires exactly the same force as pumping downwards, at least if the flow is relatively slow. If this wasn't the case, the water would move through the tube by itself if the pump was removed.
This means that when the water isn't moving, the force of gravity pushing the water down must exactly balance the force due to the pressure difference between the two ends. Because these forces cancel each other out, when you start to pump the water through the tube, the only force you have to overcome is friction, and that doesn't depend on whether you're pumping up or down. (Though if you're pumping at a high speed turbulence will occur, and then the difficulty of pumping might be asymmetrical, depending on the geometry of the pipe and the tank, in which case pumping in one direction might be harder than pumping in the other.)
Things are different if the ends of the tube are in different tanks. In this case the gravitational and pressure forces don't balance, and water can flow through the tube by itself - this is how siphoning works.