lay pipe
v. phr.— «In the first draft of every script ever written, especially the bad ones, there’s a character we writers call Sam the Explainer.…He’s the guy-gal-straight-gay-lesbian-bisexual-transgendered guy who stops the show dead in its tracks in order to explain just what exactly the hell is going on. …Among screenwriters, the Argyle-McClane scene is the ne plus ultra of explanation—what we sometimes refer to as “laying pipe.” Here’s a sample of Argyle’s Samitudinosity.» —“Explaining in the Morning” by David Kahane National Review Online Apr. 12, 2007. (source: Double-Tongued Dictionary)