Download from the Exploratorium site. Their instructions follow.
1.Leave the cap on the bottle, but peel off the label.
2.Count down about three ridges (or about three inches) from the top of the bottle. Using a scissors (or a utility knife, if an adult is doing this), cut along the ridge. Make sure you cut evenly along the edges. Trim off any bumpy ridges.
3.Recycle the bottom of the bottle; you’ll be working with the top half.
4.Take your hole punch and punch a hole as far up from the bottom of this piece as you can go. Put the straw through the hole to test the size. It should be a tight fit. If the hole isn’t large enough for the diameter of the straw, repunch the hole in nearly the same spot, making it slightly larger.
5.Cut the fingers off the glove. The glove should now look like a wide tube.
6.Cut the tube open to form a sheet of pliable material, or a membrane.
7.Stretch the membrane over the opening at the bottom of the bottle, making sure the hole- punched hole on the side isn’t hidden by the excess material.
8.Attach the membrane to the bottle with a rubber band. Wrap the rubber band around the bottle several times, making sure that the membrane’s taut.
9.Twist the top off the bottle.
10. Roll a piece of construction paper into a tube on a flat surface. Make the tube as tight and as straight as possible.
11. Put the rolled tube into the large open hole on the bottle where the cap had been. Let go of the tube when it barely touches the bottom of the membrane. It should fit securely in the hole.
12. Insert the straw in the hole on the side of the bottle and blow into the straw; your water bottle saxophone should play!
13. Tape the paper tube so it stays in place.
14. To make different sounds, add finger holes. To do this, pinch the paper tube slightly and cut out a diamond shape; repeat to make more finger holes.
The construction paper must be pushed up against the membrane to make a sound. This is the first thing to adjust if it does not work.
Also make sure that the straw is not pushed against the construction paper.
You need the instrument to be as airtight as possible. Air should only be able to enter through the straw and exit through the bottom of the construction paper.
You might want to tape the construction paper in place so that their is no air leakage.
You may need to tighten the membrane every so often.
We replaced the construction paper with a plastic sheet (photocopier or printer acetate sheet) and it worked well. It gets quite damp inside and the plastic holds up better than construction paper.