Similar to the upper decker but with a European twist. Many european toilets have the tank mounted to a wall up high with a pull cord which is used for flushing. Since the tank is high it is nearly impossible to perform the upper decker so in order to perfect the alley poop one must defecate on a transport medium (bag works fine) and then transplant this specimen into the upper tank manually. The next several victims to use the toilet are left literally with a shitty situation. The alley poop must be used with great caution and requires substantial skills to pull off correctly.
Man Peter was being a total douchebag last night"->"Don't worry about it man, there was 15 seconds left on the shot clock and I hit him with the alley poop