soil pipe

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

• noun A drainpipe that carries off wastes from a plumbing fixture, especially from a toilet.

from The Century Dictionary.

• noun An upright discharge-pipe which receives the general refuse from water-closets, etc., in a building.

from the GNU version of the Collaborative International Dictionary of English.

• A pipe or drain for carrying off night soil.

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

• noun A pipe that carries off liquid wastes from a toilet

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun drain that conveys liquid waste from toilets, etc.