I need a tube thats at least 2 1/2 - 3" long so then i can pour the powder into it and then add a little water, this way it will be more consistent than mixing in a bowl and transferring it to the tube.
That's the way I would do it - with very little water, something like a drop or two from an eyedropper. Then I would insert a 4" wood dowel that just fits into the tube and put a weight on top for compression while the water distributes throughout the powder and then drys. I wouldn't try to remove it before a day or two (but then, I may have more patience than you
).