Having built a Copper Tube Launcher, I decided to have a go at a simpler design using hose connector parts that are available from local hardware stores in the UK (I suspect that these are fairly standard on a global scale though).
By no means an exhaustive list - it should be . . .
These items are for the launcher itself. I found them in local hardware stores and supermarkets. In the supermarkets, these items are seasonal so, if you look at the wrong time of the year you may not find them. Best time is spring or summer.
You decide what you want to attach it to - I used my H-Base which the base of this launcher is designed to fit. The parts you will need are as follows:
Cut a length of garden hose approximately 8" long making sure that both ends are flat. Cut the pvc pipe so that its ands are flat and square. Make a hole in the side of the pvc pipe, approximately 2½" from one end and widen this out into an ellipse so that the garden hose can be inserted into the pvc pipe and pushed to the nearer end without causing any creases in the hose.
Push the hose through so that approximately 1" protrudes from the end. Fix the Stop Hose Connector to the end of the pipe and tighten (but do not over tighten - remember that these are only made from plastic). When it is tight, put the 1" length of pipe (with a slit up the side) onto the hose so that it is next to the connector and carefully push the hose back, feeding the hose back through the hole in the side of the pvc pipe, so that the hose connector fits snuggly on the end of the pvc pipe as in the diagram above.
Using the soldering iron, carefully make three or four, equally spaced holes in the top of the sliding section of the hose connector. These should be large enough to take the nylon or polyester cord (shown in the picture on the right) and far enough from the end of the sliding section to remain strong. Tie three or four pieces of cord to the sliding section and fasten them together at the bottom firming a loop through which you can tie the release string later.
The other end of the hose has an adaptor that allow you to pressurise the rocket. I use a car tyre (Schrader) fitting. You can either get a fitting from a car/bicycle shop or a tyre fitters or a scrap yard or you can make your own from a piece of copper pipe a woods/schrader adaptor and a piece of thick copper wire.
To make your own, cut a length of thick copper tube and cut a piece of copper wire long enough to go around the outside of the woods/schrader adaptor and bend it around, making a tight fit. File the side and the inside of the copper wire ring to give a flat, shiney surface suitable for soldering. Heat up the pieces and apply the solder until you have a seal. Let them cool down slowly until the solder solidifies before you put water on to finish the cooling process.
Put the adaptor (home made or bought) into the end of the hose and use a jubilee clip to secure it making sure that it is tight. Your launcher should now look similar to the one in the picture on the right.
Select a bottle top that has a flat end and cut a hole in it that is slightly larger than the curved part of the nozzle inlet (picture on the right). Using the soldering iron, cut grooves around the outside of the bottle top and along it making a cross pattern. The grooves need only be around 0.5mm deep (remember that using a soldering iron will make the sides of the grooves stand out as there is no material loss). Also, cut grooves in the thread of the threaded tap connector, running across the thread thus making gaps in the thread. Doing both of these will reduce the chance of the top coming away from the tap connector when screwing to/unscrewing from the rocket.
Mix up some epoxy resin and apply to the inside of the connector and the outside of the bottle top. Push the two together and make sure that the bottle top stays pushed up against the flat, internal face of the connector. Allow to dry, holding all of the time. If you tape it, the tape may move - if you clamp it, the plastic may distort. It's only ten minutes and it is vital that it is aligned properly.
Once it has dried (leave it for 24 hours), it is time to pressure test the system. Fill a 250ml bottle to the top with water and screw on the nozzle that you have made. Fix it onto the launcher and attach the air line. Take it up to working pressure plus a bit (I have got well over 100 psi) and leave it for a short while. There should be no leaks. The reason for filling with water is that water is effectively incompressible (compared to the system under test) and therefore does not hold any appreciable energy should there be a failure. Even so, you should have the launcher at at least 5 metres distance.
If everything has held, you are now ready to go.
This assumes that you have pressure tested everything.