Halve the plums and remove the pits.
Distribute the plums in 4 preserving jars (scalded and optionally rinsed with Atamon).
Split the vanilla pod and scrape out the seeds with a small sharp knife. "Mash" the vanilla seeds with a bit of the sugar to separate the seeds.
Put water, vinegar, vanilla sugar, and sugar in a pot and bring to a boil.
Once the sugar is dissolved, remove the mixture from the heat.
Add rum to one half of the sugar syrup, and add port wine to the other half.
Pour the rum syrup over the plums in two of the jars, and pour the port wine syrup over the plums in the other two jars.
Seal the jars and store them in a cool place.