Dragchute, I think that the analogy that you use is flawed because the fluid (water) you are talking about, has a weight when it is within the fluid I am talking about (air).
To carry the analogy on, if within your Vat we placed a submarine full of water, within the submarine we placed a brick that lay on the floor of the sub. Now we exert energy upon that brick and lift it from the floor of the submarine. I think we would all agree that the total VAT weight remains the same, however the buoyancy of the submarine has now increased.
Or am I talking out of my bum?