John Sykes III
I use standard paint thinner (a/k/a mineral spirits, a/k/a Stoddard solvent) with SCII (I do not use the low-odor paint thinner).
SCI is a whole different problem. Since DioSol has gone the way of the dinosaurs, you have lacquer thinner (do not use the junk they sell as HD or Lowes, go to a good paint store and get the "hot" automotive lacquer thinner), and Steve Hoxie uses xylenes (a/k/a xylol). I've tried the xylenes and it works well but is more expensive than the lacquer thinner (I get my LT at Sherwin Williams). The junk they sell at HD, Lowes and Ace is only good for cleaning brushes, spills, etc.
If you are in California, getting these solvents may be a problem, so drive over to Nevada. ScaleCoat paints (both I & II) require a high-VOC thinner to work properly. I think the latest can I got was like 800 g/L VOCs (would give a California tree-hugger a stroke!).