If the Filstars still have the intake in little sections (mine are all rather old), I have had them loosen and allow air in, which messes with the prime.
Here are some tricks that work for me:
1) Use a pump (power head, fountain pump) and pump water in through the intake. When it is pouring out through the outlet, plug in the filter. Make sure it runs. CAUTION!!! If the pump won't send the water in this way then there is a blockage somewhere. I broke one of these filters when this happened. If the water won't flow, stop pumping immediately, and look for the problem.
2) With the filter plugged in, remove the outlet from the tank, hold it as low as you can (hopefully as low as the filter) and over a bucket. Water should start flowing out. Then lift the outlet back up. Yes, it can get messy, I do this in a greenhouse, where water on the floor is not a problem. Maybe you can start the flow, then unplug the filter long enough to lift the outlet back into place.
3) Create suction on the outlet, pulling water through the filter.