In the adventure Colateral Damage, from the Codex of Adventures, a PC can gain an Ymandrake Dueling Ring. But I'm not clear on how the ring works based on the description.

The cert reads: You may transfer your Straing into this ring to a maximum of 20 Strain. If more than 20 Strain is put into the ring, it will immediately be channeled back into you, and you will suffer damage as if you attempted to cast through Strain.

The question: Can the strain be drained from the ring, e.g., between scenes or adventures? Or it an item with effectively 20 charges, and after that it's useless? Or something else?

Thanks