Tom, I agree that if you wait long enough, even one of the venturi vacuum pumps will dry out a system. But who really wants to have their air compressor running non-stop for the four or five hours it will take?
Let's assume your venturi will pull down to 28.5 inches/30,000 microns (which is probably generous). The boiling point of water is about 90 degrees F at that temperature. If it's a hot day, that venturi will do a reasonable job of drying the system. Not great, but good enough. But if it's a cool day, it is simply not going to work. To boil water at 70 degrees, you need to get below 20,000 microns, and it's absurd to think you can do that with a venturi. Given that even a garbage HF vacuum pump will pull down to 100 microns, it's really not worth it to use a venturi. The pump will do a better job faster, and use much less electricity.