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 &# 39 ; s piston plunger may be stroked several times by an operator &# 39 ; 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 . when the pump components are molded from plastics , the overall pump is lighter in weight and well suited for either desktop or portable inkjet printing mechanisms . a method is also provided of priming an inkjet cartridge pen used in an inkjet printing mechanism .