10:40 a.m. (A brief interlude of biological urgency)

“Luna!” Celestia hissed. Flecks of cum stained her lips, and the spent cock of the stallion she had just pleasured poked her in the cheek as he paused dreamily in post orgasmic bliss. “Luna!”

“Yes, sister? What is it?”

Celestia's cheeks flushed red as she lowered her voice. “Luna, I have to pee!”

Luna snickered. “Why, whatever do you expect me to do about it?”

There was a stallion vigorously fucking Celestia in the ass. With each thrust his weight drove into her, pressing her belly against the base of the stocks that supported her body and squeezing her bladder viciously. Her muscles were tense as she held back the flow. “Luna I'm serious! I really have to go! Let me out!”

Luna laughed. “Let you out? Don't be silly. You have a duty to fulfill.”

“I'm not going to pee all over the stage!”

Luna shrugged. “Suit yourself.”

“At least put up some curtains and find a bucket!”

Instead Luna moved to the front of the stage. “My dear ponies, it seems my sister's bladder is in a state of emergency. Are there those of you who would wish to assist her as she relieves herself?”

“LUNA!” Celestia shrieked in horror. At the same time, the stallion atop her yelled out “Don't piss on me! Ewww!” He scrambled off her, his cock pulling out of her anus in a sharp yank that jolted her enough that she almost loosed her urine right then. “I'm not giving up my turn,” he added belligerently.

At least four eager ponies rushed to the stage and took positions behind her. Celestia could not see what was happening, and that only served to deepen the hot embarrassment that flooded her cheeks. “Luna, please!” she said, begging her sister to halt this. There were bumps and noises as the ponies shoved at one another for position behind her.

Luna snorted in amusement. “One stallion is lying on his back behind you. You'll absolutely soak him.” She felt his hind legs wrap around her own as he settled himself into position.

She could sense the other ponies' muzzles poised before her pussy, their warm breaths washing over her. They shoved at one another, seeking a prime position, their noses banging into her rump while they snorted up great lungfuls of her pussy's smell. One of them bumped right up against her slit, and she felt herself nearly give way to the pressure in her bladder. She was swimming in the urgency, but she couldn't relieve herself now, could she? These ponies couldn't seriously want her to start peeing in their faces!

“Go ahead, Princess,” called out one of them, a mare. And then she felt a hoof with practiced skill worm under her belly and give a push against her bladder in just the right spot to overwhelm her. Her body shook, and though she squeezed her eyes shut and tried to block the flow, a squirt of her urine came spraying out against the eager muzzles.

Oh no, she thought. She felt the floodgates, having been forced open a crack, now give way entirely as the rest of the torrent came pouring after. The relief of peeing at last warred with the shame of loosing her urine in front of everypony, but all the same the release of tension was a shamefully welcome sensation.

The muzzles at her rump drew back as if to enjoy the sight of her pussy gaping wide as the river of yellow poured from it, but she felt the stallion's legs clutch around her own as he shoved his groin up into the flow.

“Oh my,” Luna sniggered. “Your pee is pouring across his balls and rushing along his shaft.” An instant later she barked out a laugh. “He's already ejaculating! Your golden river is already polluted!”

“Shut up, Luna!” Celestia gasped.

The other ponies dove in, setting their lips to the stream and swallowing it down. They pressed their mouths to her vagina seeking to drink straight from the fountain, and shoved each other out of the way. Hot streams of urine splashed everywhere, running down Celestia's thighs and spattering the faces of the ponies who seemed only too eager to taste the bitter liquid.

Though her face burned with shame, Celestia gave herself over to the flow, letting it continue until her bladder was fully drained, and the last few drops squeezed from her into the waiting lips of the ponies. However even then they did not halt, but continued to root between her thighs, tongues slurping at her to savor every bitter trace of urine. They worked their way down her legs, kissing and licking away the yellow stains, even to her spattered hooves. They lapped at the pool on the stage itself, greedily slurping down the foulness, and one of them even threw herself into it, rolling in alicorn filth until her coat was soaked.

Half despairing of her subjects, Celestia whispered to Luna “Can I bring the sun down yet?”

Luna snorted. “The day is still young, sister! Who knows what more we may discover about Equestria's ponies in the hours to come?”