Vacuum refilling is the only way to assure there is no air in the cooling system. This is super important with my Jeep JK. I was also able to pressure test the radiator with the included tools. Comes with tons of fittings and they have a few that are like the radiator cap I have and fit nicely. I was able to pull down a vacuum easily using my air compressor. Made the job alot easier and faster than the funnel.