Paul Blackwell
When I built a marble machine, the method of getting the marbles to the top of the contraption was clear vinyl tubing, and I had to bend it in two places to 90 degrees. The method they recommended was to heat the tubing in the oven (don't remember how hot) and bend it around a form. Worked fine, but had to be careful with the tubing closing up at the bend. Should work with straightening also.