When you take a deuce in the upper tank of the toilet. Leaving the owners to believe the toilet is broken, since the water comes out brown and pieces of fieces. This continues until someone either scoops it out of the upper tank or it dissolves.
Usually happens at mad crazy house parties or when someone mad dogs another person and allows them to use their bathroom.
When a man is taking a dump in the tank of a toilet while a female is sitting on the bowl taking a dump while facing him and performing oral sex on him.
Yo I was taking a shit and Tracy want to give me a blumpkin but she also had to take a shit so we did an Upper Decker Double Blumpkin