Many thanks for your instruction, Bernard. I was able to clean my DeskJet 970 cxi, because the waste ink leaked off the reservoir, as I transported the printer upside down :-( I’ve only got two additions, that I commented within the steps.

It was helpful to disassemble the main power connector to move the back panel. It is shown in picture two in this step beneath your wrist. The cable between the connector and the electronic in the box on the right side was to short to move the panel.

I had to unscrew the little red screw that holds the back panel in the black plastic base. It is shown in picture two in this step beneath the silver tongue.