Step 1) Make sure nobody's around.

Step 2) Quietly open the lid of the upper-section of the victim's toilet.

Step 3) Quietly place the lid down on the floor.

Step 4) Then take a nice shit in the upper-section of the toilet without letting anybody hear you.

Step 5) Wipe your ass.

Step 6) Place the soiled toilet paper in the upper-section of the toilet or in a drawer or magazine.

Step 7) Slowly lift the lid off the floor with your fingers under it and carefully bring it over to the toilet.

Step 8) Here's the hard part; with your fingers under the lid
slowly place the lid on the toilet. No false moves or you're screwed.

Step 9) Leave and don't let anybody see you. Just bail as quickly as possible.

Step 10) Mission accomplished.

the act of deficating in the upper tank of ones toilet leaving a foul stench undiscovered with the remnants of muddy water

The act of defecating in the upper tank of the toilet. When the next poor unsuspecting person flushes the toilet they get a bowl of beef stew. the upper decker is a weapon of terror and should only be used on people who deserve it.

As per the John Waters' film A Dirty Shame, an upper decker is the act of defecating in the tank of the toliet.

(As per my intoxication, an upper decker is my ability to write this while in the act (I'm currently the upper deck).)

using the water retaining bowl of the toilet, instead of the toilet itself.

The act of taking off the back lid of a standard toilet, hovering your anus over the opening and shooting diarrhea into the tank water. You must then wipe with TP and leave the TP in the tank. Adding red food dye to the tank is called BUD, or Bloody Upper Decker. Either with or without the dye, when the next person who uses the toilet flushes, the water that refills the bowl will be the most vile, horrific, stinky fluid known to man. Woman have been known to scream and run out of the toilet as they think their insides are coming out. Key stuff here.

While at a respected friends house retire to their restroom, stealthily remove the lid from the back tank of their toilet and steady your cheeks directly above it. Begin defecating while trying to keep as quiet as possible. When finished, wipe all remaining fecal spatter from your anus and hide the used toilet paper in the cabinet under said friends bathroom sink. When the toilet is flushed by the next user the bowl will be rinsed with your feces. A firm stool will cause repeated minor fecal rinsing, while viscous, soupy stool will flush out all at once filling the toilet thus causing repeat flushing until clean water is present.