AquaPort II Water Rocket Launcher

From the manufacturer:

Water rocketry is one of the most fun and exciting hands-on science activities around. Converting empty plastic soda bottles into high-flying rockets provides a great opportunity for students to discover important scientific principles such as Newton’s laws, acceleration, thrust, and inertia.

A second-generation launcher, the AquaPort II was redesigned to be safer than ever and still offer consistent launching for water rockets of various sizes: 2 liter, 20 ounce, and some 1 liter.