Does vp shunt reservoir fill back up after being pressed bc of its original shape or bc of fluid? if there's not a lot to drain, will it still refill?

Shape/nature: The shunt bubble is designed to stay in it's full volume size.Compressing it distorts it's shape & it wants to resume it's resting or full size.If their is no blockage it should draw fluid into it without problems.Failure to refill could mean debris buildup in the tubing or other obstruction of the flow. The fluid forming centers inside the ventricles constantly generate fluid.

Both: Yes, returns to shape. If no fluid it may remain unfilled but usually there is enough to fill them. Really only a small amount for most.