Welcome to the forum. You threw me for a bit as there is a Babelfish member too. Since you're on the vacuum side it's easy. Wondering if the vacuum gauge has a standard 1/4 NPT thread like the pressure gauges. In any case, you can tap right into the PVC pipe. Play with a scrap pipe first. If you don't have a tap you can just drill a slightly undersize hole in the pipe then use the gauge threads to cut the PVC. Smear some silicone seal or pipe dope on the threads before you screw it in for the final time. I did it with a pressure gauge for an air pressure leak test jig and it held up fine.
Al