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Bottle joining technique communicated to us by Nick Fisk

Well well, some people actually read these pages! And some of them even respond:

I have made a 8 litre rocket (4x2L). The way I used to join them together was to use 20mm PVC pipe. I drilled 2 holes in either end of the bottles. And then used hot glue to seal the pipe to each bottle. The best method I found was to glue one side of the pipe into one bottle and let the glue cool down. Then apply glue to the other bottle, before it cools down quickly push it onto the pipe, the heat from that glue, should melt the glue on the other side and they should make a pretty tight seal. I have tested it up to about 7bar and it shows no signs of leaking. Plus the bottle is still perfectly straight. I have included a picture to show you what I mean:

The green plastic is a bit of a 2l bottle to make a skirt. This makes the whole rocket a bit more solid, it has no effect on the air seal. The method takes a couple of times to get right, but once you've mastered it, it seems very reliable.

On my screen, the image is a bit dark so here is a lightened version: