Canon BJC 3000 Reference Manual page 154

6
To lock the ink tank in place, press down on top of the ink tank. Press down
until the ink tank locks in place with a click.
7
Close the front cover.
The cartridge holder returns to the home position, and print head cleaning
begins automatically.
The POWER lamp flashes during print head cleaning. When print head
cleaning is completed and the POWER lamp stops flashing, you can
resume normal operation.
Replacing the Ink Tanks
Routine Maintenance 154