The actress, who starred as Trudy Vogel on the much-loved show, told Justin Long on his "Life Is Short" podcast that the embarrassing moment happened while she was wearing the restrictive undergarment - which she described as like "biker shorts that go all the way up to your ribs (that also have a) small hole in them."
"I didn't know for the first season that you weren't supposed to wear underwear under them because they are underwear," she sighed, before recalling one time when she'd rushed to the toilet before shooting a scene "and tried to pull the hole open, but I didn't pull my underwear to the side so I'm peeing and not hearing it hit the bowl and then I just feel warmth."
"It was full pee," she laughed. But when Justin asked how she moved on from the incident, Alison replied, "I went straight to set and just dabbed it with a bunch of toilet paper. Because they're waiting on me … I don't want to lose my job."
"Mad Men" also starred Jon Hamm, Elisabeth Moss, January Jones, and Christina Hendricks. Set in the cutthroat world of advertising, the show premiered in 2007 and lasted for seven seasons before coming to an end in 2015. It won multiple Emmy and Golden Globe awards.
Earlier this year, Elisabeth Moss teased that the cast may have had discussions about a potential reunion.
When asked if the cast had considered reuniting via Zoom as other TV shows had done during quarantine, Moss answered, "Maybe we have! (Laughs) I don't know. Maybe we have had some discussions about this."
"I don't think I am in a position to officially share anything. But, yes, we are aware that people are doing reunions and we've never done one, which is so crazy. We really all haven't been together in five years. So I'll just leave you with that."