As Chip says, it's a self-priming system. Understand however, that the reason is because this is a vented system. The fill plug behind the seat is the vent. If those vent holes get blocked, priming will be difficult if not impossible. To avoid that, I clean mine out twice a year with compressed air. If in doubt, temporarily remove the fill plug 'til you're satisfied all the air's out of the system.
//greg//