Found this while searching for other guides on waste ink tank installations...
http://www.fixya.com/support/t115011-epson_680_printer_only_gives_me_blank
The "solution" post in the thread (you have to scroll down a little way) describes how to access and resolve a blocked purge tube in the CX5400 printer and if you notice the same trap door you find in the CX6600 is present in this model too..
Just thought I'd post it up as it might be useful...
_________________
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