Your Canon i550 printer may at some point show an error relating to the waste ink pads. The waste ink pads are a set of pads designed to absorb extra ink that is drained from the ink tanks during printing. If these pads start to become full, they need to be cleaned. Pads that are not emptied and cleaned could begin to overflow and damage the printer. Once the pads are cleaned, you may need to manually reset the printer to clear the error.
Stick the flathead screwdriver into the slot below the parallel port cover and gently pry the cover out.
Open the front lid and reach into one side until you find the tab holding the top cover in place. Bend the tab backward while you lift the top cover. Repeat the process for the other side until the front of the top cover is released.
Stick the screwdriver into the slots on the back, one at a time until both sides are released. Remove the top cover.
Put on the rubber gloves and remove the waste ink pads. They are located below the ink tanks.
Rinse the pads in hot water in the sink until most of the ink has been washed out. Ring the pads to remove excess water and lay them on the newspaper to dry.
Replace the pads and snap the top cover into place.
Reset the error message if necessary. Press and hold "Resume," and then press and hold "Power" until the tone sounds. Release the "Resume" button and then press it twice quickly before releasing the "Power" button.
Press the "Resume" button three times, and then press the "Power" button once. This should clear the error.