Sterilize your jars in a large pot of boiling water. If you're making refrigerator jam (it will keep nicely unprocessed in the fridge for 2-3 months), skip this step.
In a 5-quart, non-reactive pot, bring the rhubarb, sugar and tea to a boil.
Add the vanilla bean, lemon and salt to the pot and let it bubble gently for about ten minutes (on my stove, this means I set it to medium-high).
After ten minutes have elapsed, add the pectin, stir to combine and let cook for a few more minutes.
At this point, dip a spoon in the jam and see how it coats the back of the spoon. If you get a nice, even sheet, the jam is done. You can also taste at this point, to see if you like the balance of flavors. Add a little more lemon juice if you feel it needs additional brightening.
Pour into hot jars, wide mouth and rings to remove any spillage and apply lids/rings.
Process in a hot water bath for ten minutes.
Remove from water and let cool.