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 5 ft. 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.).