To decant the potion into the flask, one must have at least 6 doses of Relicym's balm in their inventory, as well as one or more potion flasks. Using the flask on the potion will open a menu to decant them. The optimal inventory setup for decanting potions is 17 4-dose potions and 11 flasks.
Only the original, six-dose potion is tradeable. Once the potion has been partially drunk, no more doses can be added to it. After all six doses are used, the flask will shatter and disappear. Flasks can be combined together, but the empty flasks will still be destroyed afterwards.