Nice builds on that site using rigid tubing. That is what I'll be replacing my Primochill flex tubing with. If your thinking of using rigid, get the clear at:
http://www.mcmaster.com/#standard-plastic-hollow-tubing/=10u5zl5
Look for the PETG type. It is pretty strong. You can find the compression fittings at a number of online stores like frozencpu.com, Xoxide.com, etc. They only sell the clear tubing at a very low price. Just use distilled water with a dye of your favorite color. I only use distilled water. You really don't need to $20 for coolant. I've been using it for years.