A piece of flexible tubing of sufficient size would do it once you establish a siphon. You'd need to make sure that it was firmly held in place so it couldn't move around, that you never let water level fall below the ends of the tube (reprime each time it does), and that the tube is of larger size than the overflow line from the tank (so you don't flood the first sump). Then you're just running water through each sump in turn. You'd have to have the tubing full of water when you place it there to start the siphon though, but that shouldn't be too tricky.