Flask of Mending

Flask of Mending is a reward purchased from the Allegiance Merchant using Talent. This item is blessed.

Use
"A strange flask that seems to double the liquid poured inside."

The Flask of Mending is a multi-use item. It is used by filling it up with Mending Potions. For every potion the flask is filled with, the flask will gain 2 uses.

To fill it up, the player must right-click the flask and target a Mending Potion. It takes 15 Mending Potions to get 30 uses of the Flask of Mending

Source
Flask of Mending can be purchased from the Allegiance Merchant using Talent.