Peel the pineapple, remove the stem, cut the flesh into pieces and crush in a hand blender. Measure 50 centiliters of the resulting fruit pulp (each 2 bottles of liqueur), mix with alcohol and rum. Put into a sealable container and leave for 3-4 days. Shake in between times.
Pour through a paper coffee filter, mix with the sugar syrup. Leave in a sealed container again.
After two weeks, decant, or use a hose to draw off the clear liquid and fill into beautifully shaped glass decanters.