I purchased a 5 foot length of 1/2 inch PVC pipe and cut it into 3 12 inch pieces and 3 6 inch pieces, leaving a 6 inch piece leftover. The PVC pipe can easily be cut with a standard hacksaw. Here's an image of our supplies.
Now connect 2 12 inch pieces using a straight connector. If you want, you could leave it as 1 24 inch piece and avoid the connector, but if you want to transport or store you launcher, it's easier to store 12 inch pieces. Now connect another 12 inch piece using the T-connector and place the 2nd T-connector at the end. Attach your 6 inch pieces to the ends of the T-connector. Cap your 6 inch pieces with caps. Place the last 6 inch piece sticking upward from the middle T-connector. It should look something like this:
Duct tape the empty two liter bottle to the end, keeping an air tight seal. Now build the rocket. Start with rolling a piece of construction paper into a tube, using the PVC pipe as a guide to how wide to make the tube.
Place duct tape over one end of the tube to create an air tight barrier.
Now add fins to your rocket using construction paper.
Next construct a nose cone.
Next place the rocket on the PVC pipe as shown a few images above. Stomp on the air bottle as hard as possible to force air through the PVC piping to launch the rocket. Turn the T-connector to launch at various angles. Our video is below.
My kids had a blast launching the rocket over and over and can't wait to take it outside! Go ahead and experiment with different angles and PVC piping designs to affect launch angles and speeds. Trust me, your kids will love this!