Bladder adventures

"You know, I think it's time you two got acquainted with your new anatomy. I wish my bladder was twenty times its current size." Jon shuddered, expecting what might come next.
Sarah walked downstairs to the kitchen, rubbing her thighs together as she went. Jon felt his labia sliding against each other, creating a frighteningly peasant sensation. He tried not to think about it too much. When she got there, she opened the fridge and took out a two-gallon jug of orange juice.
"Here goes nothing!" she exclaimed as she guzzled down the beverage. Jon could hear the glugging sound of the bottle emptying, each gulp bringing Sarah's bladder closer to full. He felt a pressure building on top of him, like someone was sitting on his back. He felt Sarah clench her abdominal muscles, struggling to hold her bladder.
Sarah waddled into the bathroom and closed the door. She lifted the lid on the commode, sat and spread her legs, giving Jon a clear view of the bowl.
"Jon?" asked Karyn.
"Yeah?"
"I'm scared."
"Don't worry. Whatever happens, I'm here for you. We'll get through this together."
"I hope you're right."
"Me too," finished Jon.
"All right, pussies! Operation Piss is ago!" taunted Sarah. Jon braced himself for what was about to happen...