bucket brigade

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A line of people formed to fight a fire by passing buckets of water from a source to the fire.
• noun A group of people who help out in an urgent situation.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A primitive firefighting technique, in which a long line of people pass buckets of water hand-to-hand from the nearest water source to the site of a fire, in an attempt to douse it.
• noun By extension, any process in which something is passed along a chain.