sunken treasure 

When one craps their pants, and then hides their fouled underwear in the tank of the toilet. A close relative of the Upper Decker.

When Mary was cleaning the bathroom after her party, she noticed her toilet tank cover had been moved. She opened it and found a Sunken Treasure left by John.

sunken treasure by The real dirty sanchez January 14, 2008

Sunken Treasure 

When the sphincter has been pushed beyond it's natural limitations and the walls of the anus collapse and fall out; anal prolapse, rectal prolapse.

When my wife gave birth to our third son, I saw her sunken treasure.

Sunken Treasure by Matilda VonWrinklebottom April 25, 2011