Go Inks C-521CMY Compatible C/M/Y Ink Cartridges to replace Canon CLI-521C, CLI-521M, CLI-521Y for use with Canon PIXMA Printers (Pack of 12), High Capacity : Amazon.co.uk: Computers & Accessories
PIXMA iX6820: Installing the ink tanks - YouTube
Canon : PIXMA Manuals : MG6800 series : Replacing Ink