Abstract: A manually actuated, spring biased, unidirectional piston pump assembly is provided for purging ink from the lines and/or nozzles of an inkjet printing mechanism. The pump's piston plunger may be stroked several times by an operator's finger to generate a pressure profile that effectively primes an ink cartridge after periods of primer inactivity. A series of baffles, comprising fingers located in an entrapment chamber of the pump, separates the ink from air being purged from the lines. The collected ink droplets fall onto an absorbent diaper material, which captures the purged ink. The pump may also be constructed as a stand-alone priming apparatus for priming a pen cartridge before installation in an inkjet printing mechanism. Preferably the pump components are constructed for snap interfits which facilitate ease of assembly and decrease costs associated with manufacturing.