Don't know what the factory uses in the kits now , but on my Series 5 I use clear tygon tube with little cork balls that I painted dark green with fuel proof paint. My tubes do get a bit cloudy but i can always see the cork balls floating in the tube. Also at annual when I fold the wings I found a heat gun with a low temp setting clears the tubes up . I usually change them out every couple years. I would be very wary of substituting the tygon with acrylic or anything untested. Years ago the skystar kits used a plastic tube and they always failed and you can imagine the mess in the cockpit not to mention the danger if this happened in flight. Bruce N199CL