I pushed the antifreeze side down with a pencil eraser, installed the fittings and left the plastic tube real long, fill the top of the isolator and get all the way full, no bubbles, put the plastic tube in a cup of antifreeze and suck, stop a few inches from getting any in your mouth, hold your finger over the end and put the cup end into the isolator and seal it up.
The tube can then be put wherever and the antifreeze will stay put, cut off what you don't need and hook to the gauge.