allow me to most humbly disagree. a small passage means high reynolds #
loss and inefficiency.

Quite right. Good vacuum system design is to use large diameter tubing. In
a practical sense, just make sure your pump has a flow rate much higher than
your system's leakage rate. It is easier to use an oversize pump that will
keep ahead of the leaks than it is to use a miniscule flow pump and track
down leaks. A 1/3HP, 5cfm, pump developing up to 28.5" Hg should be
sufficient for anyone's work clamping setup and not be too hard on the
pocket book. HVAC repairers use such a pump and they aren't too expensive.
Dan