Because of the forces involved inside a typical rocket, and because PET plastic is very hard to glue, there are only a few existing glues that are suitable for the job. The most commonly used is PL Premium construction adhesive, but VISE and a small number of others can also be used.
Splicing is not as easy as joining bottles using a Robinson coupling, is permanent and is less predictable at which pressure it will fail, but it has the advantages of virtually unrestricted internal flow and potentially long pressure bodies can be made this way.
The technique presented here is based on previous work done by other rocketeers:
In the following video tutorial we present a technique called 'symmetrical splicing' for joining two bottles. The same technique can be used for making much longer bodies. The join is just repeated for each section.
For more water rocket instructions visit: http://www.AirCommandRockets.com