I already discarded the idea of using a pouch.
When you try to close a pouch, a fairly substantial air bubble is fatally left in the spout, no matter how close you try to level the liquid to the edge of the spout. This is due to the diameter of the spout and the fact that a liquid tends to form an arc at the surface of a spout.
I think the solution is to have a very thin and long spout (see my post #28) on a squeezable bottle, so that when you squeeze the bottle before capping it, whatever air is left in there, say a 1 millimeter long bubble, it will still be a cylinder 1mm tall and 2 mm wide, which is a really tiny bubble.
To empty the bottle out, one would uncap it, let air in through the spout, remove the cap and quickly pour it out.
Please see the photo on my post #28.