I'm going to make the switch to CAT ELC and have read topics and watched videos regarding flushing the old coolant out, but when it comes to refilling I haven't found much. I've watched videos that people fill up the system by filling the overflow and allowing the vacuum of the system to pull the fluid through, then driving and refilling as needed. I've also seen people use vacuum fillers that go over the opening in the overflow bottle. Which is better, causes less damage to the system, and has the least risk of vapor lock?