I’d Love to Know the Origin of “Sitting with the Bathtub”

I first heard this phrase when playing euchre with my grandma, grandpa, and aunt. My aunt and I were playing against the octogenarians, and my grandparents were beating us pretty badly (In that first game, I think they were up at least 4-6 points before we scored any). My grandma said she guessed they were “sitting with the bathtub.”

I honestly couldn’t stop laughing (what a phrase for playing cards!), and the game stopped while they explained to me that there was an old superstition that the pair of players sitting parallel to the bathtub would always win. I would love to know how that superstition started! It was true that night but not the last time we played (when Grandma and I were sitting parallel to it). My personal superstition is that whoever is playing against me will win…

Seriously, though, if anyone has a clue how this phrase started, I’d love to hear it. I can imagine someone making a silly joke about it during a long night of playing, but how exactly did it catch on?