Hrrm, might be a bit difficult to automate the Tooltip thing for Multiblock Parts.
As for Infinite Testing, have you tried inserting an NEI 111 Stack into a GT6 Mass Storage? That will fill it up 100%.
I tend to duplicate Fluid Containers using NEI and just use a canning Machine to empty them, but now that you say it, I should probably let the Fluid Display Item be used as a “fill up Tank 100%” thing using the Tiny Funnel or Cap Nozzle.