I have several of these. Is it not sucking water up the tube at all? The water level has to be with in 6 inches of the top of the tank.
You do need to fill the chambers with water, both of them, all the way up until it flows into the tank. If you have done that, and it is still not pulling water up the tube, then I would bet the impeller is not correctly seated in the tube. One of my Whispers will not hold onto the impellor unit when I put the tube/impellor onto the hole in the box where the impellor is supposed to sit. The impellor drops into the hole by itself, and then I have to blindly drop the end of the tube into the hole and hope the end of the impellor ends up in the center hole of the tube. If not, water is not pulled up the tube. This sometimes takes several tries until it hits the right spot.
Does that help?