A temporary view the anus takes after the act of anal sex. When the penis (or penis shaped device) is pulled out of the ass, the anus is sometimes left temporarily gaping wide open. This allows for a clear view into the ass thus creating the affect you might get when looking down a stovepipe.
After a few seconds the anus will usually contract back to normal shape.
Millie: Holy cow, after finding my mom's video tapes in her closet. I watched my Dad totally stovepiped her. I mean it looked like you could see all the way to China. No wonder my Mom was walking funny the next day.
Holly: You're Dad is totally hot. He could stovepipe me anyday.
Millie: I'll ask. Maybe my Mom could film it.