Sterilize your jam jars and be at the ready. Put two spoons in the freezer.
Bring the rhubarb and grapfruit juice to a boil in a large heavy pot. Turn it down to a simmer and allow to cook for several minutes until the rhubarb softens.
Meanwhile whisk the sugar and pectin together.
Add the strawberries to the pot and return to a boil. Turn down the heat and simmer several minutes until the strawberries are soft. Then whisk in the sugar and pectin and bring to a boil yet again. Stir to avoid scorching and to beat down any froth or foam. Turn the heat back down to a simmer, and pour a little jam onto the back of a frozen spoon. Run your finger through it - if the path stays open you are done, if it doesn't, simmer awhile longer and then re-test.
Fill you jam jars leaving at least 1/4 inch headroom. We filled to the bottome thread. Wipe the rim and seat the tops (those will have been in hot water, right?) and secure with the rings. Put all of the jars in the canning pot and boil for 10 minutes. Remove them from the pot and allow to sit undisturbed until completely cool, at least 12 hours. Check your seals and then either hoard or share, it's up to you!