Upon further review and questions about crappy drawing I am now thinking that the tank systems would be better with hydraulic piston concept. I will post a better drawing if I can make it. so to amplify, the oil pushes the piston and changes the bouyancy and displacement.
as the oil is pumped from the junction box to the tank/tanks lined up by 3way valves the oil will be evenly drawn from the tanks that are lined up to equalize with the junction box. the piston should be have two seals on it.