Finding a listing in urbandictionary.com does not mean that people actually use the phrase as it's defined there.

Student or Learner
Oval Office
A toilet
OMG WTF! You clogged the oval office!
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Does "oval office" represent "toilet" because of the shape?
It also seems to mean the following.
a slang term for the vagina
Mr. Lincoln loves to work in the Oval Office
Finding a listing in urbandictionary.com does not mean that people actually use the phrase as it's defined there.
I am not a teacher.
I would assume it refers to the shape of the toilet bowl.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.