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1.
the act of a male individual shitting or pooping in the upper deck of the toilet while a girl goes down on you (aka; sucking your penis), while she releases poop out of her butthole into the lower deck bowl of the toilet.
Jeff to Randy: Dude, bro, Jerry definitely just got some of that double decker blumpkin action dome piece from that random B with the STDs.
Randy to Jeff: Real nice, real fuckin' nice.
by Lambeaux + Jerry November 09, 2008
 
2.
Takes two people, one takes a dump in the tank of a toilet while the other faces backward on the normal toilet seat dumping while giving the tank dumper head.
Yo, eff those tool bags, they wouldn't give us any beer so Crystal and I pulled a double decker blumpkin in their master bathroom and rolled out! Try flushin that bitches!
by Vern1234 March 09, 2010
 
3.
When someone is doing an upper decker and the person on the lower decker is is giving head and takeing a shit at the same time.
I walked into two people doing a Double Decker Blumpkin in your bathroom.
by sick mo'fo December 06, 2012