I have used lacquer thinner to thin Floquil for almost 50 years. It's essentially the same as Diosol, except a lot cheaper. It's also great for regular ScaleCoat, Dullcote and Glosscote, Pactra, Testors, and Humbrol enamels, and SMP Accupaints. I also use it to clean my airbrush and regular paint brushes. As David notes, it does "attack" plastic, but properly applied on styrene with an airbrush, it works fine. That plastic attacking property is useful, too, as it makes an excellent solvent cement for styrene.
I buy mine in gallon cans, then decant it into smaller metal or glass containers, depending on its intended use. For styrene cement, I use it from an old Testors cement bottle, with a brush in the cap. For really fine work, a small, good quality paint brush works well. For larger gluing projects, I use it from a quart can, applied with a 1" brush.
No matter whether you use Diosol or lacquer thinner, work in a well-ventilated area (and preferably use a spray booth vented to the outdoors when painting) and definitely wear a two-stage respirator.
Wayne