The act of defecating inside the water tank of a toilet.

Step 1: Go to the home of your mortal enemy. Ask to use the bathroom.

Step 2: Approach toilet and remove the water tank lid.

Step 3: Step on the sides of the toilet and squat over the water. Carefully take a massive dump. Wipe your ass and dispose of toilet paper in the trash bin.

Step 4: Place water tank lid back on the toilet.

Step 5: Escape.

What happens? With each resulting flush, it will fill the bowl with a chunky brown water. Its the gift that keeps on giving :)
Lady mere mere: Just took a massive upper decker

Bro: Are you serious? Thats messed up. You really know about upper deckers
by t-bozz January 28, 2013
39 more definitions
10 Words related to upper decker
Top Definition
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
Also referred to as 'Going Up Top,' the act of taking a shit in the tank of a toilet. Common courtesy not to flush. Used TP should be placed inside drawers, magazines, or the tank itself. Feel free to throw in any other items you can find in the bathroom during the process.
"Man this party sucks... I'll let 'em know how I feel with an Upper Decker"

"Dude!! You shit in my toilet" -> "Where else did you want me to go?" -> "Not in the top part you fuck!!"
by ShitBrick February 24, 2004
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
The act of defecating into the upper tank of a domestic toilet.
When they started playing charades, I took an upper decker and made a quick exit.
by afokenr March 25, 2003
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
The act of removing the upper lid to a home toilet. leaving an imense amount of defacation inside. the next customer will go and then flush your shit into the bowl, repeatedly.
while in ohio, the clarion hotel wouldnt give us a room because we werent 21, so ryan anson gave them an upper decker
by friend July 30, 2003
To take a crap in the top section of one's toilet so that when it is flushed, poo water flows back into the bowl.
Every a-hole deserves an upper decker!
by King Flump April 10, 2003

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