For my manufacturing class, the final group project is to design and produce a yo-yo. My group chose a "washing machine" theme. Each side holds water inside a clear plastic bubble, using a clever double-interference snap fit.
AssemblyThe blue inner ring pushes outwards on the white base part, holding it snug against the clear bubble. The black outer ring pushes inwards on the same white part, effectively locking the blue inner ring in place. A 1m drop will sometimes cause the black outer ring to pop off, but the blue inner ring always stays in place and holds the water seal tight.
We used CNC mill and lathe to make aluminum molds for the parts we had designed in CAD. There are three injection molded parts, one thermoformed, an o-ring and some small laser-cut clothing items that float in the water bubble. We produced over 50, and they snap fit together.