Ink box full - Brother DCP-J140w Compact Color Inkjet All-In-One Printer

First thing you need to do is to reset it. If you reset it and continue to use it without completing the process of cleaning it out completely you will have the waste ink tank overflow causing major damage to the machine, your desk it is on and possably the carpet, curtains and anything even close to touching the machine and subsequent items being touched by the machine. Ink on a non-porous material will travel a very long way damaging everything in it's path.

Menu - Black Start - Up Arrow x4
This needs to be done in the space of about 5 seconds.

On the screen should now read Maintenance.
using the up and down arrows get the LCD screen to read the following: Between each number you need to press the 'OK' Button
8
0

This is now in Function 80 which is the system log.
Use the black start button to get to the log for Purge or Flush counter it is normally somewhere in the region of 25th in the list.

Once you are on this item. Use the up and down arrows and the OK button to do the following sequence:
2
7
8
3

This will reset the purge/flush counter to 0

Press the Stop button to return to the Maintenance on the LCD screen point.

use the up and down arrows and ok button to do the sequence:
9
9

This will exit you from the Maintenace Mode.

Now you will have reset the counter but you are not done yet. We are up to the hard part now and the messiest.
You need to clean the Waste Ink Tank out. You have to dismantle the printer to get to the waste ink tank. This requires a bit of knowhow to do it without damaging the machine but you can't get the knowhow without opening up the machine. This will require removing several screws and unclipping various parts of the casing then removing several cables to allow the different parts to seperate. If you are unsure or don't want to risk it don't do it as damaging the machine or the electronics inside the machine just means shelling out for a new printer and rather than spend the time to reset the machine and cleaning it out only to replace the machine because of a broken part on dissasembly or reassembly you may just want to replace it outright. It may be in one of two places. Depends on the machine. The cleaning process is the same for both systems.

The easiest machines have it in a box behind the paper feed mechanisim. Disconnect the two feed tubes from the box and remove the box. Break the plastic seal over the Waste Ink Tank material.

The not so easy machine has the waste ink tank underneath the main chassis of the printer. You have to lift all the components if the machine up to get to the waste ink tank. Do this to access the material.

Remove the material and clean it out using lots of running water squeezing as much ink from the material as possible. Wrapping it in Newspaper to absorb water put it on the ground and stand on it to squeeze any water out. Place the material aside for a couple of days in a warm dry place to completely dry out. Put the material back in the respective waste ink locations as shown above. Then reassemble the machine and test.

Failure to complete the cleaning process I stress again WILL result in the overflowing of the Waste Ink Tank. Proceed at your own risk.