soil pipe

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A drainpipe that carries off wastes from a plumbing fixture, especially from a toilet.

Century Dictionary and Cyclopedia

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

Wiktionary

1. n. A pipe that carries off liquid wastes from a toilet

GNU Webster's 1913

1. n. a pipe or drain for carrying off night soil.
2. A pipe or drain for carrying off night soil.

WordNet 3.0

1. n. drain that conveys liquid waste from toilets, etc.