Filling balast problem

I have a outback with the factory ballast system. This year the the ballast under the rear seat does not want to fill. The pump is running, the valve is open, I checked for obstructions at the intake. Any suggestions?

I often have to be driveing 20 mph or so to get the pump "primed" and then it starts filling.
It doesn't take long once you have it started filling you can stop.

I have the same problem with my single bag ballast. The dealer said, as did Bruce, that sometimes you need to get the boat on plane before the pump is primed and starts to fill the bag. I have also found that if you turn the pump off, to empty, to fill, sometimes that will start the bag filling.

Thanks! I'll try this.