As it turns out, our visit to the last university on the short list of prospects common to all four of us revealed it to be just right! Especially once we learned that it had a chapter of the sorority that our mother had been a member of and that its current leaders were actually expressing an interest in SNBs for this chapter's housing, our decision was even easier! When I asked Mom how they'd even heard about them, she told us that she had announced their existence on a site for alumnae as soon as they'd passed final testing. As it turns out, sanitary nanobots fit in really well with the sisterhood's main secret, which was that members were encouraged to develop looser-than-normal standards of privacy among each other as a means of bonding. Previously, this amounted to little more than leaving bathroom doors open even in situations when outsiders would almost certainly close them, but if the negotiations succeeded, my mom's invention would enable it to be taken to a whole new level. When she was telling us this, I got the feeling that Mom wasn't quite telling us the full story, but I figured she was just preserving at least some of the surprise for rush week, so I shrugged it off. The possibility of not having to give up our convenient self-relief habits as soon as we started college was enough to make us all look forward to the big move even more than we already were.
In the meantime, we three sisters and Beth had graduation and a whole summer to enjoy! Our commencement was quite long, as these things tend to be, with a keynote speaker giving a speech so drawn-out and dotted with thinly-veiled platitudes that I think even he was bored by the time it finally drew to a close. That was probably why, after the last student had gotten his diploma and the whole event was adjourned, the first thing Lina did after we piled into our car was hike up her gown, yank her pants down, and immediately start pooping on the seat. "Geez, I thought that guy would never shut up!" she groaned as a banana-sized turd promptly emerged from her butthole and forced its way out while she hovered a couple of inches above the cushion. In rapid succession, two more brown masses slid out of her body, the third one only slightly smaller than the first two.
On her part, Kala had been dancing a bit towards the end of the ceremony, so I wasn't surprised at all when she simultaneously tore her gown and pants out of the way and promptly soaked her own seat with a torrent of pee that gushed out of her almost as if from a fire hose. She sighed deeply. "I don't think I've ever had to go this bad! I actually considered just wetting my pants and hoping the gown would hide it!" She moaned as she pulled her panties and jeans back up and collapsed on her seat a few seconds before Lina did the same.
Although Beth's home bathroom had been fixed, she didn't stop availing herself of our unorthodox facilities whenever it was more convenient, which happened quite frequently, given how often she was at our house or in our car over the course of summer vacation. However, one particular night, it seems to have been her turn to shock us. The four of us were at a drive-in theater seeing the latest Disney remake. The convenience of SNBs was probably never more obvious than they were at the outdoor cinema, since we could eat or drink all we wanted and relieve ourselves right where we were without having to miss anything. No annoying bathroom breaks for us! Heck, as the climax mounted, Kala never even took her eyes off the screen as she raised her butt a bit off her seat, lowered her pants, and took a huge dump. A single soft moan was the only indication that she really even felt the three brown, bratwurst-like turds pressing themselves out of her body. Probably from sheer experience, she seemed to instinctively know how many seconds to wait after pulling her pants back up before she could lower her butt back onto a clean cushion.
That was unremarkable. What took us three sisters by surprise was what happened as the movie drew to a close. Beth had the biggest crush on the actor playing the male lead. Apparently, this particular flicked showcased his appeal especially well, because as the credits started rolling, our blonde best friend had begun playing with herself. At first, she seemed content to repeatedly squeeze her 38C breasts together while we looked on in amusement. Then, she started massaging her nipples between her thumbs and index finger, likely frustrated that she had to do it through the fabric of her top to avoid being indecently exposed through the car window. Barely a few seconds before we finished the last of our snacks and would've otherwise started the engine to return home, she blurted out, "Oh, screw this!" She kneeled between her half of the back seat and the driver's seat, practically tore her jeans and panties down, and promptly started stroking her genital slit. "Oh," she sighed in tentative relief.
"Are you serious?" I sputtered, half-amused and half-shocked.
"Oh, c'mon!" she breathed. "With everything else we do right in front of each other, do you really think masturbation is a big deal?" Her stroking accelerated and then morphed into more of a pussy-probing motion with her fingers. With that her eyes drifted closed as her thrusts grew deeper and faster. "Ah!" she squeaked, signaling that some threshold of nascent pleasure had been reached. The ramming of her fingers into her vagina grew even more frantic, and she rested her cheek on the driver's headrest as she started rolling her pelvis back and forth. When those rolls turned into sharper and seemingly involuntary twitches, I knew she had reached the point of no return. "Oh, crap, I'm gonna cum!" she managed to announce raggedly. "I'm cumming!" Indeed, she climaxed barely a second later, with a final, teeth-gritting warble and one last pelvic spasm. My sisters and I all watched in astonishment as she basked in her bliss for a few more seconds before simply pulling her pants back up and reclaming her seat with a sigh. "So, let's go home, shall we?"
The spell finally broken, we could only giggle at her nonchalance. "Geez, Beth!" said Kala. "That was bold, to say the least! Even with our weirdly low privacy standards, it never would've occurred to us to do that!"