Does anyone know the technique and hardware needed to fill a smaller tank of CO2 from a larger one? I have two smaller kegerators that use 5lb CO2 tanks and I just bought a larger 20lb tank for a bigger freezer. I can get the tanks filled for $12.50 each plus 50 cents a pound. So 5lb tanks are $15, but 20lb tanks are only $22.50. I'd like to fill the little ones from the bigger one and save the $12.50 every time.