How to Reset Canon MP780 - Waste Ink Tank Reset Procedure

1) Press the following keys in sequence: Copy-Menu-Scan-Copy-Scan.
The display will say:
SERVICE MODE
#1 SSSW

2) Press the > key (also labeled +) six times.
The display will say:
SERVICE MODE
#7 PRINTER

3) Press OK.
The display will say:
#7 PRINTER
#1 SSSW

4) Press the > key (also labeled +) four times.
The display will say:
#7 PRINTER
#5 INK ABS CAPA

5) Press OK.
The display will say:
SUCTION
XX (where XX is how full the waste ink tank is as an integer percentage)

6) Change the XX to 0 by entering 0.
The display will say:
SUCTION
0

7) Press OK.
The display will momentarily say:
SUCTION
DATA ENTRY OK
and then will quickly change to:
#7 PRINTER
#6 CDR ADJUST

8) Press the Stop/Reset button

And the printer is back to normal.