Regarding the potential vacuum level of a shop vacuum, I can offer the
following.  I have an older Sears Craftsman shop vac, top-of-the-line
at the time.  I think they advertised something like 2.5 horsepower.
But beware, because most vacuum manufacturers give a horsepower figure
that is impossible to achieve given the wattage that they draw (they're
calculating peak horsepower based on inrush current during motor start).

But I digress.  This vacuum will lift a column of water four feet.
So you're looking at something like 50 inches of water.  No big deal.
Shop vacs get their lifting power from volume.  They move a lot of air.

Ray Fairfield

 [ A "lot of air" is right!  Paul Freiling and others have successfully
 [ used the turbine pump of the shop vacuum cleaner to power a calliope.
 [ But the same turbine could hardly meet the suction needs of a Duo-Art
 [ piano, which may demand 70 inches water column suction for a big
 [ "crash".  -- Robbie