I haven't found any good alternative to good light and good optics. The lighting is tricky, too. You need to have light that illuminates the tubing but doesn't impair your vision. When I fill the infusion set tubing with the attached reservoir, either in or out of the pump, I hold up the length vertically with a good light behind the infusion set. Even then, spotting the fill-line as it moves up the tube is subtle.
I wear my "see-close" glasses, of course. I make an extra effort to eliminate all bubbles in the reservoir before I connect the infusions set.
It would be nice if the insulin was tinted a bit to make this exercise easier.
Good question and I don't think my answer is very satisfying.