My in-laws had one of these sitting around doing nothing so I've grabbed the chance to get this unit documented and added to the instruction set:
http://www.octoink.co.uk/store/pages/Epson-CX3200.html
As you'll see this is a variation on the rear trapdoor routine with a small twist... Nothing too tricky though.
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Printers: (Canon) MP500/830, MX700, iP4000/4200/4300/4500/5200, iX4000(A3) (Epson) C84/86, D88, CX6600, R285/800/1900 (HP) K550, K850, K5400, L7680