Ok, I've already done a lot of what you describe, but I will redo it more systematically as you describe. One problem: the vacuum pump definitely seems to allow air into the setup as soon as it's turned off. I used numerous methods to "isolate" or remove it when preparing to try to hold a vacuum. So, the lack of holding a vacuum described above applies without the vacuum pump. With it---it always loses vacuum when turn off. Didn't seem right, and I guess it's not?