This oilskin pouch holds more than it should, including a small breathing tube that extends from the inside.
Wondrous Item 1,000 gp
This belt pouch contains 1 hour’s worth of air, which remains fresh indefinitely. Once the air in the pouch has been consumed, you can refresh the supply by exposing the open pouch to any supply of breathable air during a short rest.
Published in Adventurer's Vault 2, page(s) 76.