I call this the "manifold". This is what you connect the bicycle pump to for pressurizing the rockets. It accepts a normal American valve fitting (schraeder), or the European kind (presta). I use a good bicycle floor pump with a guage that goes to 140psi. The right angle brass valves are used to direct air to either the quick disconnect garden hose launcher or the other launcher.
Here's the hold-down and release mechanism for the standard launcher, shown in the hold-down position. Flat stock aluminum was used to make a collar that fits over the bottle's neck flange. By pulling the string, the lever is pulled, pulling the collar's narrow opening part off of the bottle's neck flange.
This is the hold-down and release mechanism in the released position.
Here's the quick disconnect garden hose launcher. When you pull the string for this one, the lever pulls a string which goes through a pulley and then pulls the collar down on the quick disconnect fitting. These fittings have a built in spring to pull them back again.
A close up of the release lever, pulley and string.