Jeff was stuck, and in a bad predicament; He tried pushing against Megan's clitorus, and used his knees as additional force. His right leg got caught inside of her vaginal opening, and it tightened in response, causing his leg to remain trapped.
"Come on... I have to be able to get out of here!" He pushed harder against the roof of her inner labia, providing more sexual pressure and - Due to her age - an increased need to pee. He kept trying, unable to get out.
He could feel her sit down, her legs straightened out as her labia forced closed around him. He was pressed further against her genitals, with his nose inside of her urethra. He couldn't see it, but she had pulled her panties down, trying to see what she felt down there. Due to her smooth labia being closed, however, she was unable to see Jeff.
Trying to find what was causing the feelings though, she poked the outside of her slit, which pushed Jeff a bit further in. Although muffled, he could hear a small conversation between Diana and Megan. "What are you doing, Megan?" Diana asked, with Megan responding with "I can feel something down there, but I don't see anything."
Megan stopped poking, the words "Oh well, Guess it's nothing." emanating from above. He still tried to move, causing more pressure buildup. He couldn't tell, but Megan could; Her panties were pulled up, the words "Uh oh, Gotta go potty!" coming down as she tried to get to the bathroom.
Jeff pushed harder, as Megan entered the bathroom. She sat down and peed, unknowingly blasting Jeff in the face. He was forced into drinking some of it before he could react, as the hot urine warmed his entire body. After he got his mouth closed, it mostly went past, sliding through her closed lips.
The flow stopped after a minute, Jeff feeling the toilet paper press him in again as Megan wiped. Jeff was left speechless about the situation; He was trapped inside his five-year-old sister's labia, although he didn't quite know the name of it, and he was just pissed on.