Rainbow Dash was going on a camping trip and had invited Pinkie Pie to go with her. They had arrived at the campsite ten minutes ago and set up their tent.

It was a hot day today, so they both drank a lot of water. They'd gone for a walk through the forest, and walked by the entrance to a cave.

Once they had finished their walk, Rainbow Dash said "So, how about that pushup contest I suggested?"

"Sure! It'll be fun!" said Pinkie Pie.

They had packed their exercise outfits for the contest, so they put them on. (In case you forgot: Rainbow Dash's is a yellow shirt and skintight white shorts, and Pinkie Pie's is a yellow shirt and skintight teal shorts). They began doing pushups, and keeping count of them.

...

Twilight Sparkle was studying an old ancient ruin. She was wearing a sparkly dark blue skintight outfit because she had just been in a fashion show hosted by Rarity, and then read a book that mentioned the ruins and gave its location. She was so excited she had flown straight to the ancient ruin without changing out of her outfit.

After an hour of exploring the ruin and taking notes, Twilight wiped sweat from her forehead. It was a boiling hot day today, and most of the ruins didn't have a ceiling. Her outfit wasn't making it any cooler, and was already damp with sweat. She didn't have enough room in her bags to place it, so she left it on. Noticing a nearby pool of water, Twilight took a cup out of her bag, filled it with water from the pool, and drank it more times than she could count.

...

"77... 78... 79... 80!"

Rainbow Dash did her 80th pushup, but Pinkie Pie was unable to finish hers and collapsed to the ground.

"I win!" said Rainbow Dash.

Pinkie gave Rainbow a hoof bump. Both were panting and dripping with sweat after doing so many pushups on a hot day. So, they both took out their water bottles and drank them, refilling them at least twenty times in a nearby spring.

They laid down in the shade and relaxed for a while. After about twenty minutes, Rainbow Dash said "Let's explore that cave we walked by."

"Okey dokey lokey," said Pinkie Pie, and they entered the cave. Pinkie held a flashlight in her mane as it began to get dark.

...

Twilight could have flown up the stairs of a pyramid structure, but she thought it was more fun to walk up the stairs. Once at the top, she got a view of the ruins. The view was amazing.

Until, the urge to pee hit her. She had drank a lot of water. She tried to run down the stairs, but tripped and fell down the stairs. She lay sprawled at the bottom of the stairs for a few seconds, before she stood up. She had managed to hold it in, as she wasn't desperate yet, but the fall had made the pressure greater.

Twilight searched the ruins for a bathroom, but as expected, there wasn't any sign of one. So, deciding she'd seen enough for today, she flew high into the air in search of a nearby town. She saw one, and flew straight towards it. As soon as she touched down on the ground, she noticed that the train was boarding. She decided she would take the train back to Ponyville and use the bathroom on the train.

She boarded the train. There were no other ponies in sight. As the train started leaving, Twilight looked at the town, and realized to her dismay that this was Dodge Junction. This train didn't have a bathroom, otherwise Pinkie Pie wouldn't have had to wait until they arrived. So, much like Pinkie before her, Twilight sat with her legs crossed, a panicked look on her face.

...

"Face it Pinkie, we're lost," said Rainbow Dash.

"I told you we should have turned left at that fork," said Pinkie Pie.

"Well..." Rainbow Dash began, but she was interrupted by a jolt from her bladder. All the water she had drank was beginning to affect her. "I gotta go... bad!"

Pinkie giggled, until she too felt the effects of all the water she drank, which was more than Rainbow. "I gotta go pee too!"

"We need to get out of this cave and to the outhouse fast!" said Rainbow Dash. They ran as fast as they could, searching for the right tunnel.

...

Twilight fidgeted where she sat. Now she really needed to go. She didn't think she could hold it another minute. With each moment she could feel the pressure growing stronger.

Then the train stopped. The sudden jolt caused a small jet of pee to come out of her, forming a small wet spot on her outfit. She was barely able to hold the rest of it in. She looked out the window. There was no town nearby. The train had broken down.

Twilight couldn't wait for the train to be fixed. She didn't have a moment to spare. So she opened the window, climbed outside, and flew toward the train's destination as fast as she could.

The town had just slid into view when Twilight felt the crotch of her outfit grow wet. She immediately stopped and stood on the ground, trying to hold it in but it was no use. Twilight was wetting herself again. She couldn't help but sigh of relief as the legs and rump of her outfit became soaked, forming a big puddle under her.

After 20 seconds, Twilight finished peeing. She was blushing with embarrassment, but maybe it wasn't so bad. No one had witnessed her accident, and she felt a sense of relief after holding it for so long. All she had to do was get back to her castle without anyone noticing.

...

Rainbow Dash and Pinkie Pie ran through the cave, randomly turning each time they reached a fork in the road. Both mares were in desperate need of a bathroom, but the entrance to the cave was nowhere in sight.

"Rainbow Dash, stop!" said Pinkie, and she sat down with her legs crossed. "I can't run anymore! I don't think I'm gonna make it!"

"Wait, do you hear that?" said Rainbow Dash.

Pinkie listened, and nearly lost it right there. They could hear the sound of running water. They turned around a corner to find a river.

"We saw a small waterfall come out of a rock wall!" said Rainbow Dash. "This river is our ticket out of here!"

"Are you sure?" said Pinkie.

"Positive," said Rainbow Dash. "Let's go for a swim! After you!" She slapped Pinkie Pie's butt, and this made Pinkie lose control. As Pinkie began peeing in her shorts, she felt embarrassed at first, but remembered this wasn't the first time Rainbow Dash had seen her wet herself, and knew no one else was ever going to find out. So, she decided to just find this funny. She giggled at the feeling of the warmth spreading, as the pee flowed down her legs.

Rainbow Dash watched, her heart racing. Pinkie Pie was already wetting herself, and she was about to jump into the river, so she couldn't see why not. "Oh no, I can't hold it any longer!" said Rainbow in a not-very-convincing tone, and she let go and peed herself. She let out a long sigh of relief as her shorts changed from white to yellow, growing wetter and wetter - the sweat had long since dried off them - as torrents of pee flowed down her legs.

Pinkie giggled a bit. She knew exactly what Rainbow Dash was doing.

They peed for about 30 seconds before they finally stopped, Pinkie Pie only a few seconds before Rainbow Dash. Rainbow blushed a little, sure Pinkie could tell how much she enjoyed wetting herself, but all Pinkie said was "Well, it's time for a swim!"

They jumped into the river, which took them out the cave and down a small waterfall, the same one they had walked by. They climbed out of the pond, shook themselves off, and decided to relax for the rest of the day.

...

Twilight's outfit was in the wash and she was taking a bath. She had made it back to her castle unseen. None of the other ponies were around - she remembered Rainbow Dash saying she was going on a camping trip with Pinkie Pie - and Spike was asleep. She could now relax that no one would ever be able to tell the Princess of Friendship had wet herself, except Rarity, that one time at the beach, but as Rarity was in the same situation she knew she'd never mention it again.

Author's Notes:

I thought I'd do one last chapter revolving around these three ponies, since I wanted to give them with as much detail as Rarity. I didn't really want to put Fluttershy through this again. It took me a while to come up with a new scenario for them, but I did.

This is the grand finale of this story.