Water colors

I am not a painter, but I notice when watching water colorists on Youtube, and when available, PBS, that artists will sometimes thin paint out that they had initially put on a little thick on the painting using a dry brush, or at least a brush with no paint on it.. As I said I'm not a painter, but I'm trying to learn how to use Corel Painter 11 watercolors. How would I do that same thing digitally, thin out a paint using a dry brush or a brush with no paint on it?