New answers tagged design
To rephrase: Is there a way to make two pipes join together in an removable way that would be no more than 10mm thick with nothing inside or outside the extended planes of the existing pipes in a way that is water tight? No. BTW- the image in the link provided is for a key lock for desk drawers and the like.
To prevent stuff from sliding off the poles, yet keep the same look, you can try spraying the exposed poles with some kind of clear rubberized coating like this
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