Down the street, a turquoise trash truck awaited its close-up.
And the attention of one well-connected toddler.
"Axel's obsessed with trash trucks," explained McElhenney of his and Olson's oldest son, who turned 2 on Sept. 1. (His brother, Leo, was born April 5.)
And so his father came up with an episode about a Philly garbage strike so Axel could see a trash truck?
"Specifically so we could have a trash truck on set and he could spend at least three or four hours with it," said the St. Joseph's Prep grad, who created the show about friends who run a bar in South Philly. He and fellow executive producers Day and Howerton continue to write for it.
"When he gets here, you'll see his reaction to this trash truck. It's going to blow his mind."
In the meantime, it's back to the van for McElhenney, where Day has spent part of the morning hurtling out the rear doors, on each take jumping or falling a little differently as the crew adjusted pads below, trying to keep them out of the shot while protecting the actor.
"Hopefully, I don't break my rib, the way I did in Season 4," said Day, referring to the "A Very Sunny Christmas" special, where "they were blowing fake snow on us - it was hard to actually see - and I jumped as I high as I could . . . backwards and I curled up in a ball and I missed the pad and just landed on the floor. And cracked a rib."
"Charlie, just so you know, this is the softer part," said a crew member, pointing to a section of the pad.
So he's a little more careful these days?
He laughed. "Yeah, I want to at least make sure I land on the pad," he said, adding that he does "something risky and stupid every season. And the older I get, the more stupid it seems."
Willful stupidity remains at the hilarious heart of "It's Always Sunny," which returns Thursday with "Pop-Pop: The Final Solution," an episode about Dee (Olson) and Dennis (Howerton) and their dying, Nazi grandfather that demonstrates once again that its characters, as McElhenney likes to put it, are "never learning anything or growing or changing."
But there's nothing stupid, or haphazard, about the making of the show, which is shot more efficiently than most, with five of the season's 10 episodes in production at a time.
When McElhenney decided, for Season 7, that his character, Mac, should gain 50 pounds - to buck the sitcom convention that TV characters, unlike the rest of us, tend to get more attractive over time - he didn't settle for a fat suit. But he did consult a nutritionist recommended by the Phils' Chase Utley to pack on the pounds as healthily as possible.
Most of the extra weight's now gone, but McElhenney's no less conscious of the need to differentiate "Sunny" from other long-running comedies.
There's more at work in "The Gang Recycles Their Trash," the episode for which the "Sunny" crew had temporarily trashed a lovely neighborhood, than a treat for his son.
"We come into the first scene and we're talking about a plan to make money that sounds very [familiar] to us and we realize it's something we've already done, it's something we've already tried," McElhenney said.
"And we realize that's very common in the eighth season of a television show, also. And so instead of pretending that just doesn't exist, we wrote to it and had the characters realize, well, just because we've done it before, doesn't mean it doesn't work. In fact, if we just make better decisions all the way through it, then maybe it'll work this time," he said.
"The original plan [from Season 4's "The Gang Solves the Gas Crisis"] was to sell gasoline door to door, which kind of makes sense. So you never have to go to a gas station . . . The problem is that the characters aren't smart enough to fully execute it," he said.
"So we have a parallel story where there's a trash strike in Philly," and the characters have a plan to capitalize on it, one that is, as usual, less than politically correct.
McElhenney, 35, "was a little kid" in South Philly during the city's 1986 garbage strike, which ran for 20 days in the heat of July. "But I remember piles of trash everywhere."
And now he has a son who lives in Southern California and is, he said, "obsessed with garbage, garbage trucks, garbage cans."
When Axel arrived a few minutes later, he wore a Phillies cap backward and an intent expression as he sat on his mother's lap, high above the street in the driver's seat of the Volvo trash truck.
As Olson and McElhenney took turns in the cab with Axel, showing him how the claw that picks up the trash bins worked, he was wide-eyed, but seemed more interested in beeping the horn.
Clearly, his father wanted to play with the claw. "I'm into it, too," he admitted. "He doesn't care as much about the arm."
Later, after Axel had been lured from the truck and the couple returned to the production's base camp so Olson could feed Leo, I asked McElhenney about the transition from being a single guy in his 20s with an idea for a TV show that actually ended up getting made to heading into an eighth season - with a ninth already ordered and talk of a 10th - with a wife and kids.
"Yeah, we're full-fledged grown-ups now," he said.
One reason the season's starting a little later this year was that "Kaitlin was pregnant with Leo. Although she gave birth in April, we still wanted to have enough time that we could both spend not sleeping and being up three, four times a night. And being able to focus on him and not being worried about anything else. And that was a key factor. And then Charlie was doing this movie, so he was in Canada for a while, and Danny was doing a show in the West End of London," he said.
A 10-episode season allows the actors time for outside work and gives McElhenney and Olson time to "raise two kids," but "the schedule is still fairly extended because we're writing the episodes and we're editing the episodes [as well as acting in them]. So it'll still take seven months, eight months out of a year. But the true advantage of a 10-episode season is that we can stay fresh, and that from a creative standpoint, we can still surprise people."
Though McElhenney's working on a couple of screenplays in what he jokingly calls his "spare time," his weekends, he said, are now off-limits.
"You can very easily start to compromise that and say, 'Well, I'll just work this Saturday.' Or, 'Well, I'll just work a few hours on Sunday.' And we realized that that's a slippery slope. And if you just make a rule that Saturdays and Sundays, no matter what, are completely and totally off-limits and just devoted to spending time with your family, then you can't go wrong."
But from the somewhat less family-friendly perspective of "It's Always Sunny," "it's still about what we find interesting and funny to talk about. And really, watching other television shows and trying to explore what isn't being explored elsewhere" because "people are afraid, oftentimes . . . to go into areas that are considered dark or untouchable. And we feel like those are the areas that we want to hit."
Is there anything he would have done eight seasons ago that he wouldn't now?
McElhenney didn't even pause. "I don't think so. And if you've got any ideas, let me know. Because we're always looking."
Contact Ellen Gray at email@example.com or 215-854-5950. Follow her on Twitter @elgray. Read her blog at EllenGray.tv.