Can't guarantee this will work, BUT don't deviate from this procedure. This worked on my Canon s630. Taking the printer apart is not that easy, you must work on the basis that the printer will be write off before start stripping it down.
Waste Ink Tank Full Error Reset
1. Turn off printer
2. Hold down Resume button and press Power button.
3. Keep holding down Power button and let Resume button go.
4. Press Resume button 2 times then let BOTH buttons go.
5. Green lights will flash and then stop blinking.
6. When green lights are solid, press the Resume button 4 times.
7. Press the Power button and the printer should turn off, if not, press the Power button 1 more time.
8. Done.