Bite the Bullet.
Some artists slit the tube, spread it open and dab color from the hard chunk of paint inside. They risk ruining good brushes. If you can get chunky paint out of the tube, put it in a palette well with a couple of drops of gum arabic. It may become useable again. But if it's gritty, there isn't much you can do to restore it to its original consistency. There are artists who regrind the paint, mixing it with binder to a creamy consistency. Wouldn't you rather paint?
Another problem with using old paint is that there are a some colors that undergo chemical changes in the tube and become discolored. Also, you won't find discontinued colors on the market, so why use colors you can't replace?
Paints that dry up and become crumbly are usually student colors. Buying student paint is a false economy. The tube may be larger or cost less, but you'll need more paint to achieve anything near the intensity of good quality artist pigments. So, ante up and get the good stuff. You'll see the difference in your watercolor paintings.
Please, throw away those wretched, rock-hard, twisted tubes and use fresh, good-quality paint.
I'll have a rant on paper soon.