Measure the sugar into a bowl and set aside.
Place the rings and the lids of the jars in a small pot of simmering water, and heat a large pot of water that will serve as your water canner.
In a large, heavy-bottomed pot, mix together the rhubarb and the pineapple, and heat over medium-high heat until the pineapple juice begins to simmer, 1-2 minutes. Reduce the heat to medium, cover, and simmer for about 5 minutes or until the rhubarb is just beginning to turn tender. (It will fully soften and break down later.)
Stir in the pectin, and bring the mixture to a full boil over high heat, stirring regularly.
Stir in the sugar, and return to a full, rolling boil (a boil that does not stop even when stirred), stirring constantly, for one minute.
Remove from the heat. Stir in the apricot brandy or peach schnapps, if using. Allow the jam to sit for 3-5 minutes, stirring regularly. This will prevent floating fruit and will allow the foam to subside. If any foam remains, you may skim it off.
Ladle the mixture into clean jars to within 1/4 inch of the rim. Wipe the rims, and put on the lids. Tighten the rings just until fingertip tight.
Process in the hot water bath (jars should be fully submerged) for 5 minutes. Carefully, remove jars from the water, and allow to cool to room temperature. Check the seals. When the center of the lid is pressed, it should not move. If it “clicks” in and out, the lid has not sealed and should be stored in the refrigerator.