Craig Tube adapter for any straight-sided tube, including Eppendorf tubes.

An adapter for any straight-sided test tube to turn it into a crude Craig Tube for extracting crystals.

If you got crystals in a tube mixed with liquid, slap one of these on top, shove a cocktail stick in the bottom and centrifuge it (with the stick at the bottom)

After a short time you have nearly dry crystals in the tube and the liquid at the bottom of the centrifuge container.

Obviously the choice of filament material needs to be OK with the solvent you used.

You will need to re-scale the .STL in your slicer to get it to JUST fit your tubes.
It should not leak when it is upside down, but leak a few drops if you swing it hard in your hand (test using water).

My first try with it : https://www.sciencemadness.org/whisper/viewthread.php?tid=83542#pid522683