A slight twist on the original blumpkin
The double upper involves a male taking an upper decker
while a female is taking a dump in the main bowl of the toilet while facing backwards. While all this is happening she is blowing him.
My buddy and his girl would have a few drinks after a night of eating hot wings. When they got home they were both so horny and had to shit so bad that it would inevitably turn into a double upper blumpkin.