ORIGINAL: Triple Se7en
When it gets rocky, spread it out thinly on a covered table & let it dry in a non-humid environmentbefore putting it back in the jug. That sub-powder, much like real blackpowder, can become moisture-contaminated and re-dryed with supposedly no ill effects. How true that is - I don't know!
I know its true for Black Powder. Water is used in mixing the ingredients of black powder. If water is used in the mixing of subs I don't see why that wouldn't be true.