A simple double cork adapter that is supposed to hold the bottles together mainly by the tight fit. But use glue to make it permanent. It's sized for small bottle of spirits, "snappsflaskor" :P and it seems to fit. I think it might be hard to clean the support material if you print the whole piece with support so I have also uploaded a "half" version; print both halves and glue them together. Have yet to try it with sand, so I have no idea if the hole is a good sice. I had a thought that it might be possible to use salt?