Close the inlet valve. Remove the perspex cover on the pump, fill from a hose, replace the cover, then simultaneously open ONE of the valves - Fond (drain), for instance), and run the pump. When the pumpfull of water has emptied, simultaneously close the fond valve and turn off the pump, remove the perspex cover and repeat the process again, and again, until you can hear the progress of the returning water - it'll probably take fifteen minutes or so, dependiong on how far the water has to go in the pipes. You may have to repeat for the other inlet valves to get the air out of them. Speed is of the essence, to maintain the suction.