Taking a shit in the upper tank of a toilet. Also known as "2000 Flushes Brown" and "The Gift That Keeps On Giving"
The people at that fondue party were such fuckin' pricks that I had no choice but to give 'em the old upper tanker.
What idiots call the "upper decker".
Idiot: I gave that ho an upper tanker!
Some Guy Who Knows His Shit: You mean an upper decker?
Idiot: Yeah, whatever.