When dropping a deuce, taking a dump, dropping the kids off at the pool, etc...the fecal deposit after flushing leaves an artistic swirl of streaks and smudges behind in the bowl resembling sections of marble.
The act of two males putting their ball sacks inside a cloth bag as you would hold marbles and tying it closed.
Person 1: i really want to have our balls together more than usual
Person 2: how bout we start marbling them?
Person 1: yes please, i love it when you're nestled inside me marbling our balls.