After you take out all 4 ink tanks, swing up the mid-grey coloured section on top of the ink tank carrier. It is 'L'shaped, but like an L that has been flipped, and then rotated 180 degrees. It runs along the top of the ink tank carrier and down the right hand side. It is hinged on a horizontal axis.
Then, with the back of your hands together, reach inside the ink tank carrier with your two index fingers and press outwards on the sides of the carrier. With the slight pressure from your fingertips, pull the carrier slightly forward and then up. The carrier should then come out easily.
Re-installation is that in reverse - very easy.
I have had my MP700 (4 tanks) for about 5 years, and have mostly used DIY ink tank refilling. For a long while it was fine, but eventually started printing black badly, with streaks and missed patches. I had the printhead replaced (realised later how easy it is to do myself, thus could have saved the service charge). The problem returned not long after. Finding a solution has been VERY frustrating.
I have used isopropyl alcohol, both pure, and recently in rubbing alcohol solution (!@#$%^& government regulations have stopped the local pharmacy from selling pure). Also ammonia solutions, window cleaner, etc, all with limited success.
Today, getting desperate, I took out the printhead (see my earlier post of today's date), and placed it upright it on several layers of toilet tissue. I then thoroughly flushed the print jets with rubbing alcohol by applying it, drop by drop, to the fine metal mesh where the ink tanks contact the printheads. (I used one of the needle nozzle bottles that the replacement ink comes in). It takes a while, as the alcohol sometimes soaks through slowly. Keep going until almost no ink stains the tissue.
I then took the print head to the kitchen sink, boiled up a jug of water (our water is quite soft, ie not a lot of mineral content), and slowly poured the whole jug directly onto the metal mesh ink contact pads. If you keep the printhead upright, you shouldn't get any water on the electrical contacts on the back). By the end of the jug, no more ink was draining through. I replaced the printhead in the machine feather, and it seems to be printing nearly perfectly. Fingers and toes are all crossed.
My local printer repair technician says I may need to get the 'purge unit' replaced or cleaned at some time, apparently quite a job.