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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.
Plumber: It looks like you have feces in your toilet's tank.

Victim: It must have been an upper decker.

Plumber: Yeah right. Its already clear that you're stupid enough to shit in there!
by Mike_Litoris June 27, 2011
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2
An upperdecker is when you poop in the toilet tank of someones bathroom, its the gift that keeps on giving
i was at this party and they tried to kick me out so i gave them an upperdecker
by Nick June 16, 2006
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3
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.
My friends x-girl friend had a party and she left whith some other dude who looked like the fonz "Heyyy!". So I took it upon myself to leave her an upper decker
by The Mad shitter May 14, 2003
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4
The upperdecker is a prank that you can pull on a friend or loved one, or more likely someone who deserves it. An upperdecker is defined as defecating in the upper tank of a toilet, allowing it to fester for as long as possible and sending a chilling brown residue into the bowl upon each flush.
At a party where they run out of beer one might like to leave an "upperdecker" to show their disapproval.
by Grant Herman August 31, 2004
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5
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).)
"I started doing upper deckers, shitting in the top tank of the toliet, where no one would ever look to find the odor . . . "
by iloverobots01 January 08, 2006
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6
using the water retaining bowl of the toilet, instead of the toilet itself.
that beyotch pissed me off, so I ate 3 large burritos, took some Ex Lax, went over to her house and left her an upper-decker to deal with.
by Amanda Huggankiss August 02, 2006
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7
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.
The upper decker was rejoiced by all who were present.
by A Tortured Soul March 04, 2006
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