Cut the long piece of PVC pipe into four pieces. The lengths do not have to be exact, so estimation is OK if you don’t have a tape measure. Cut one piece to around 3 feet long, 2 pieces to 1 foot long and one piece to around 4 inches.
Drill a hole in the center of one of the PVC end caps. This should be a big enough hole for the tube end of your valve stem to fit through. Compare the size of various drill bits to the end of the valve stem to determine the best one to use.
Apply barge cement or bathtub sealant to the circular base of the valve stem. Apply the adhesive material to the side of the circular base with the stem extending up from it. Push the valve stem through the hole in the end of the PVC end cap. Push it in so that the adhesive forms a bond and keeps it in place.
Stick the two 1-foot pieces of PVC pipe into the opposing ends of the “T” shaped PVC connector. Use PVC glue to stick these pieces in place. The free end of the “T” connector will have a female thread adapter. Insert a male thread adapter into this end. Glue the end caps onto the free ends of the two 1-foot pieces of PVC pipe. One end cap will have the valve stem poked through it.
Glue the 3-foot and 4-inch pieces of PVC pipe into the two openings of in elbow connector. Stick the remaining male thread adapter into the end of the 4-inch PVC piece. Attach the free end of the 3-foot piece of PVC pipe into the opening at the bottom of the “T” connector. The construction should have the three longer pieces of pipe lying on the floor, and the shorter piece pointing directly upward.
Wrap some electrical tape around the male thread adapter on the end of the 4-inch piece of PVC pipe. Wait until the glue has dried before you do this. Ensure all of your connections are tight, and lay the “T” connector on the ground so that the short pipe points directly upward.
Move the construction outside. Fill a plastic soda bottle a quarter of the way up with water. Attach the upside-down soda bottle to the end of the 4-inch piece of PVC pipe. Try to minimize water spillage. Connect a pump to the end of the valve stem. Pump the pump and wait for the soda bottle rocket to take off. This should happen when there is around 30 pounds of pressure per square inch. The bottle will fly around 30 feet into the air.