Hopefully you've got it worked out by now. Airlocks seem to be pretty common, especially between rinsing out. But, the bleed valve down by the shifter you explained always eventually got things primed for me.
I haven't had any problems with mine, but the best advice I could give is to keep the system flushed out and clean after every use and put some antifreeze in the tank when you're not spraying. I like to think this keeps the pump lubricated a little allowing it to circulate through the aggitation hose, along with most importantly not letting the pump run dry during granular applications.