Jonesing,
I think Phil's advice with the dishwasher is good. I don't have a dishwasher so I boil the jars for ~10 minutes. They air dry super fast, and they're still pretty hot when I fill them; but like Pease says, I don't worry about whether a slight cooling vacuum forms.
Lately I've become more interested in jarring to retain the original condition of the tobacco than in aging it. As I noted elsewhere, after two years of aging, only McClelland's 5100 improved remarkably well. Va flake, Vaper, and Navy flake didn't show much improvement.