Subject: What is the difference of boyancy between air and vacuum filled containers?

National Geographic has an item for sale: an hourglass inside a tube of water.
In trying to guess why the hourglass rises in the tube, as the sand in the glass 
falls, we came upon another question: which has greater buoyancy - a container 
filled with air, at normal air pressure, or that same container with a vacuum?

I'm the answer to our question has to do with the air being compressed 
(slightly) under the sand, and decompressed, sightly, above the sand.

Re: What is the difference of boyancy between air and vacuum filled containers?