My twin 50's and Selpak manifold were more negative than I liked, so I added a piece of 4 inch PVC pipe with closed ends to act as a buoyancy tank. It means that I had to wear more lead, but now my rig and I are each closer to neutral.
I like my Viking dry suit because it has no inherent buoyancy. Once I have compensated for squeeze, it is neutral. But I do have to adjust my weight belt to the underwear for warmer or colder water.
---------- Post added September 24th, 2013 at 11:36 AM ----------
A student in a certification class had a novel idea. Instead of wearing lead on a weight belt, wear sponges. When the sponges get wet they are heavier, but when you get out of the water, the water drains out and they are not heavy anymore. Apparently, he was not acquainted with Archimedes.
there was a similar claim a while back on ScubaBoard where someone indicated that they add water to their BC to be more negative.