Effluence

"I don't believe it," said the skeptic tank.

The sewage treatment plant explained its inner workings.

"And these so-called 'sewers' are all underground, you say?" said the skeptic tank.

"Mostly," said the sewage treatment plant.

"How very convenient," said the skeptic tank.

"Gaaaghhh!" said the sewage treatment plant. "You're a dinosaur!"

"And you're full of shit," said the skeptic tank.

The sewage treatment plant gurgled in exasperation.