Watch the depth of the depression on the water surface. Try to keep it constant. Use the mouth walls as shock absorbers when you let each fresh breath into your mouth. Find reeds that are naturally soft. They grow in rich soil inside the shadowy parts of a protecting bush.
Hard reeds require more air pressure.
Peel the thin outer glaze with a very sharp small knife. You might have to repeat after a while. Remove the inner membrane by rubbing with a small butt stick. Cut into 1-2 cm long tubes. Put the mold stick inside the tube with the thick part under the knot.