Step 1: What you need.
Step 2: Cut out the middle section of your bottles.
Dry the sections out with a soft cloth, and let air dry. You do not want any moisture in your green device. Otherwise, its gonna mold.
Step 3: Hot glue together.
Step 4: Make a small hole in your cap.
Step 5: Add sugar.
If it is longer than five minutes (or desired time), make the hole in the top slightly bigger (a very slight change in size will result in a drastic change, so use cautiously!).
If it is shorter than five minutes, add sugar.
Get it so it is exactly five minutes (or desired time) in length.
Step 6: Cut a huge hole in the other cap.
Step 7: Glue, glue, glue!
Then, flip one bottle on top of the other, and glue the caps together.