combination waste and vent system

combination waste and vent system

A special system of venting in which the waste piping is purposely oversized; intended as an economical means of providing adequate protection of fixture traps against loss of seal in extensive installations where the individual venting of fixture drains would be impractical or uneconomical; serves both as a waste pipe and vent pipe.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.