To try to stretch the center portion of a section of liner material by inflation, you need to first seal the cut length up on both ends. One thing that works well for this is a pair of rubber stoppers, one solid and one with a single hole in it. Note they are installed backwards, fat end first, for a better grip, and held firmly with rubber bands.

A small basketball type hand pump is used for the inflation. Many such small pumps come with several screw in tips, one of which is a plastic straw affair that will fit right into a stopper's hole. You want the liner material to inflate in the middle as near as possible. Some liner material is not well suited for this, because it is quite thin on one side relative to the other and will balloon out on the thin side only. It will probably just burst.

12/03