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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The act of taking a dump in the tank of a toilet.
Step 1: Quietly sneak into the bathroom unseen
Step 2: Carefully remove the top of the tank. Note the porcelain tank top is very delicate and will shatter if dropped

Step 3: Climb on the toilet, drop pants and sit on the tank. Imagine you are a bird sat uptop your nest, sit very softly or else the tank may break and the operation will be compromised

Step 4: Take a monster shit. I'm talkin like a goddamn mudslide out your asshole

Step 5: Whipe and throw the tp in the tank too for good measure and put the top back on

Step 6: Return to the party and act like nothing ever happened, if you leave right away you will draw suspicion to yourself
Step 7: Enjoy the host's reaction when they see that Mount Vesuvius just exploded in their toilet tank
Friend: Yo did you hear, Julia is having a party this Saturday
Me: I dislike her very much, I'm gonna drop an Upper Decker at that party
by bowelsmovin June 25, 2017
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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.
"I was working a night party at that rich cunt's house. As the party was ending, I asked the beeotch if I could make a sandwich. She yelled at me in front of her guests that I will "eat with the rest of the hired staff at the end of the night!" A simple no would have been fine. For a thank you gift, I pumped a gallon of milk into my lactose intolerant ass and dropped and Upper Decker that cunt's main bathroom. Later, I Bloody Upper Decked (BUD) the upstairs daughter's fine china toilet. After that I raw dogged one of the workers and bailed, yo.'
by Dick Smartly July 3, 2014
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The act of shitting into the tank (or upper portion) of a toilet. Done as a prank, it results in at least four foul flushes (also known as a "3-F qualifier") afterwards.
"Man, I'm gonna fucking puke."

"Dude, how come?"

"Man, someone dropped an upper decker in the toilet, and the water splashed my ass and sack."

"Dude, that sucks."

"Man, I think I got a piece of corn stuck to my sack!"
by papamikedelta October 24, 2009
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Yo last night I took an upper decker in Jim’s toilet!
by FamousJew October 29, 2020
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A toilet prank, whereby someone defecates in the refill tank (water closet), causing each additional flush to deliver brown, poopy water into the bowl.
Jim was being such a jerk at his party, so I went upstairs to his bathroom and dropped an upper decker in his toilet.
by bodythunder November 12, 2008
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When attending a persons home of who you dislike, take a shit in the toliet tank instead of the bowl. This is by far going out of the park and into the upperdeck where it will not be known until long after you depart their house.
When your wife makes you go to her boss's party who you would like to kill, go to the bathroom and leave him an Upper Decker and you'll know who the joke is really on.
by Noah Burnett April 28, 2006
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