We stuffed some paper in the top bottle of our rocket, along with 4 rocks. We tried a test launch with 800 volume of water, the launch angel was 45 degrees, and the result was 64.52 meter. It was good beginning, and it can fly farther if it did not hit the trash bin. After the first test launch, we change its mass from 178.4 grams to 189 grams by adjusting the stuff at the top. We also use tap to fix some "wound" on the bottle. We want to make the lip rounder, so that it can face less air resistance.
Look more in my gallery.