Refill Canon Pixma CLI-8 und PGI-5-Cartridges: Step 2: Insert the cannula
Now take the cannula and insert it into the hole you just drilled. Guide it as straight as possible along the bottom of the cartridge, right through the sponge.
What you are aiming for is the hollow chamber of the cartridge. The two chambers are connected by a small opening, and that´s what you are trying to hit.
Once inside, you can see the end of the cannula inside the ink-chamber.