Straight Line Sumo Pump Priming

I have a tsunami pump for my flyhigh sacs and a straightline sumo pump for 2 other ballast bags. The tsunami pump works awesome, but the the straightline cant seem to get a steady pumping stream. Has anyone else had this problem? Is there a trick to priming? I even sucked on the end to get all the air out; it pumped for a little bit then stopped again. When it works, it works great, but I just can't get it to empty/fill consistently.