Ho to reset MX850 waste ink tank

Solution to reset waste ink tank (error 5B00):

• Power off printer
• Hold Resume button then press and hold POWER, the beeper will sound once. 
• Hold POWER and release RESUME
• Press RESUME twice, then release all buttons
• When the indicator lights steady, press RESUME three or four times. The indicator should be orange.
• Press Power to set data

Link:

• More about Canon MX850