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15.
A lady's ass that is so flat and wide that it resembles a tank like structure. If she layed down you can use that tank ass for a table.
Slut bend over so i can ram rod your tank ass then eat some butt
by gerbil April 17, 2003
 
16.
Ass with marks left from sitting on the tank (toilet) for too long
John-"Dude, you've got tank ass!"
Bruce-"WHY THE F*CK ARE YOU IN MY BATHROOM?!"
by Empty Health Bar August 06, 2004