To do the sex act; copulate; screw: If you're up all night, laying pipe, you won't be worth a shit to me on the court/ About eighty a them's gonna lay more tube than the motherfuckin' Alaska Pipeline(1967+ Black)
To specify; spell out: You can't just infer that; you gotta lay pipe(1970s+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Examples from the Web for lay pipe
We're up against the real thing in the morning, and may as well begin to lay pipe.