This is an area that is problematic with the canon cartridge/printhead design.
Thus the seal between the cartridge exit ports and printhead is minimally stressed. The reason for this is to minimise the pressure needed to draw ink into the cartridges from the reservoirs. One thing I have done with regards the IP3000 and this CISS unit is to elevate the CISS reservoir about 40mm above the desktop.
After periods of inactivity (days) often a few inches of air is observed. A few inches of air will often make its way into the lines above the cartridges but this doesn't seem to matter. With the pinch roller engaged - photo 3 - you can them move the reservoirs relative to the printer unit. Have used the selective image CISS in MP730 and IP3000, and it works well as long as you are meticulous with setup and then the beauty of CISS is that you don't have to keep fiddling, just keep the reservoir topped up. Then do the same for each line that needs bleeding. When all the air is bled then replace the elbow into the top of the cartridge. Priming can be done by having the cartridges exit ports sealed and the ink reservoirs at the same height, pinch roller not engaged and remove the elbow from the top of the cartridge and elevate the reservoir slightly until the ink runs along the line and drips out the end into a dish. I took the photo of a CISS just removed from its packaging and then one I had already installed in a IP3000. If it is greater than a few inches then it pays to reprime these lines. I have 5 of these and when they arrive after shipping there is often air in the line. The uninstalled system is not the same CISS set as the installed system.