On Christmas Eve in 2015, I stood in a stadium parking lot, mingling with a group of Oakland Raiders fans before the team's holiday game. I desperately needed to pee.

The call of nature wasn't unexpected — we had all been helping ourselves to a cooler full of Coronas and Pacificos. But when I asked where I could find the closest restroom, dreading what fumes and mutated microbes I would soon encounter in the smell shack of a porta-potty, the tailgaters did not direct me to some far corner of the parking lot. Instead, they pointed to the asphalt alley created between two idling vehicles. In plain view of passing fans and patrolling police officers, they had set up what can best be described as a piss bucket, already sloshing with questionably colored liquid.

"There?" I asked, eyeing the bucket. Great!

As any stadium-goer knows, and as thousands of National Football League fans will surely remember this weekend during the season's first slate of games, gastrointestinal and urinary inconveniences are to be expected at live sporting events. Long lines at the (often gross) restrooms are further compounded by the fact that all beer-soaked and foam-fingered fans seem to pick the same exact moments to seek relief — halftime, timeouts, the usual breaks in the action. My appreciation for this stadium-based struggle only deepened as I spent a year on the road visiting dozens of sports venues nationwide for book research. Really, if I learned anything about American stadiums, it was this: You can forget courtside seats, luxury suites and all-you-can-eat areas — an empty bladder is the most desirable commodity on game days.

In other words, pee every chance you get.

I'm not alone in this opinion. Some fans go to great lengths to abide by this unwritten stadium rule, and piss buckets are just the beginning. At a Saints game in New Orleans, I met a man in the upper deck who — because of his creaky knees, which hurt every time he traveled up or down the steep Superdome steps — had developed a unique strategy for relief. The evidence, a discreetly placed water bottle, was beneath his seat. And although I didn't conduct any pat-downs, I know some fans go even further, strapping portable urinals, known as Stadium Pals, to their legs, so they can go at will in a stadium — or anywhere, really. (This portable urinal includes a funnel, a tube and a plastic sack. The female version is known as a Stadium Gal and is described by the company as a "female urinary pouch.")

[Stadium metal detectors don’t keep you safe. They just make you miss some plays.]

Some fans show less discretion. A Wisconsin native told me about his first trip to Lambeau Field, home of the Green Bay Packers. He was only a kid, waiting at an entrance gate to get into the historic stadium. A few ticketholders nearby started to feel droplets, which was weird, because the sky was clear. When they looked up, they saw a fellow Packer Backer on an upper concourse, producing a huge golden arch.

Of course, accidents can happen. In fact, one fan I met in Philly was confident that urinary mishaps were universal experiences. "Everybody has been in a porta-potty and you have to cut your underwear off," he said. "I have been there. I've been sitting in a porta-potty and somebody opens the door, and you piss all over yourself trying to close the door. Welp, get my knife out, cut these off."

And it doesn't happen only to fans. Football players have admitted to peeing in their uniforms during games, and last season, a Washington assistant coach was spotted on the sidelines hunched over a paper Gatorade cup. (He was almost certainly not the first.) Meanwhile, outside the stadiums, ticket scalpers and curbside merch vendors cut deals with local businesses so they have facilities at the ready. Such alliances are to everyone's benefit, because public urination can become a serious problem, as it did in the residential neighborhoods around Barclays Center in Brooklyn soon after the building opened in 2012.

No one wants to plod through a puddle of someone else's waste, but renegade piddling is more than just gross; it's dangerous. At Rio de Janeiro's famous Maracana Stadium, for instance, tradition long dictated that fans could relieve themselves in the stadium ramps instead of trudging all the way to the restrooms. That way they needn't miss any of the action on the field. This led to severe structural problems. In 2000, it was discovered that the urine was eating through concrete and corroding the stadium's steel skeleton. In response, the venue instituted an "anti-urine" unit to police the ramps and concourses.

Maracana officials had hesitated to modernize the restrooms, because Brazilian fans have a tendency to tear out toilets during post-game riots. At least one person has been killed via toilet bowl at a soccer match in Brazil — not at the Maracana, but at Arruda Stadium in Recife — when inflamed fans started hurling uprooted commodes.

[Learning to love the secret language of urine]

Old habits can, indeed, be hard to kick. At Wrigley Field, where Chicago Cubs fans were forced to urinate in their beer cups at the start of the 2015 season when off-season renovations bled into Opening Day and restroom wait times stretched more than an hour, fans demanded that officials keep many of the men's room troughs instead of upgrading to individual urinals. To longtime fans, the troughs represent a kind of heirloom toilet culture, passed from father to son. As one fan put it to me, "If I'm going to come to Wrigley, I want to piss in a trough."

In recent years, stadium architects and operators have tried to address some of these issues at American venues. Now, they consider things such as "toilet ratios," with guidelines from "potty parity" laws, which try to legislate away longer restroom wait times for women, and advice from groups such as the American Restroom Association and the World Toilet Organization.

According to such groups, inadequate restroom facilities not only pose public health risks, but also make it impossible for people with medical problems such as colitis or urinary-tract infections to enjoy events in stadiums and other public places. Which is to say nothing of the very real physical and psychological conditions that can lead to men "choking at the bowl" (a real term) in stadium restrooms, i.e. needing to pee but being unable to squeeze out a drop.

Lest you think I'm being overly scatological, toilet talk really does permeate every inch of American stadiums, from Wrigley Field's vintage center-field scoreboard, wherein staff members have to pee into a funnel because of a lack of plumbing, to the seats behind home plate at Fenway Park, inhabited by seemingly prim and proper New Englanders.

That's where I sat for a Red Sox game in June 2015, flanked on one side by a young Boston faux intellectual, dressed in skinny jeans and a beanie. He spent a full inning explaining to his date the ways in which baseball is an existential game. As that monologue droned on, a woman on my other side, who wore reading glasses and a Patagonia fleece — she had the look of a middle-school English teacher — told me about the time she squatted behind a dumpster after leaving the ballpark.

"Hey," she said, with an Albert Camus-like shrug. "When you gotta go, you gotta go."

Twitter: @rafi_kohan