Dookie Train
A Dookie Train is another way of saying you have to take a massive dump since it will take so long.
Megan: "Gosh, what's that stink?"
Elizabeth: "Oh I have to take a massive Dookie Train."
Megan: "Oh great, it's going to be a long one!"
Elizabeth: "Oh I have to take a massive Dookie Train."
Megan: "Oh great, it's going to be a long one!"