When using Gorilla Glue for standard woodwork in my shed, I've found that old, stiff glue in the bottom of the bottles responds well to microwave heating. It comes out nice an runny and doesn't seem to be any less effective as an adhesive when set. This applies to both dampened and non-dampened use. A word of warning - use safety glasses (in case the bottle "pops" when you take the lid off, wear gloves to keep it off your skin and be VERY careful in heating it up (I increase the microwave exposure only 10 seconds at a time as there is a risk that it will be too hot and too runny to handle). I can completely empty a bottle this way.