Fukiya (3.5e Equipment)
From D&D Wiki
Fukiya, a usually black-stained Japanese blowgun, is considered to be a Ninja weapon and can be used as a breathing tube for hiding underwater. The user can remain indefinitely no deeper than 5ft. below the surface of any body of water deep enough to fully submerge the user. Should the character dive deeper than 5 ft. they must hold their breath as standard, and must surface completely to clear the water from the Fukiya before breathing from it again. A character using a Fukiya as a breathing tool cannot perform an attack or cast spells requiring a verbal spell component, but can swim at half speed. While submerged in this way the user gains a bonus to Hide checks determined by individual DM based on lighting levels and appropriate cover (reeds or other river grasses can obscure the Fukiya's tip, ect.).