At one time the expression "pull a train" was in reference to a woman who has sex with several males in a row. The expression today, having been used in several gay porn flicks isn't restricted only to women. It stems from a quote by Lawrence Paros in The Erotic Tongue (1984): ' The lone-woman in a cluster fuck or club-sandwich (mid-20 th C.) has to pull her weight as well as that of her friends while pulling-the-train (mid-20 th C.), a succession of men who, like a string of boxcars, had to be coupled and uncoupled .' :biggrin1:
One Example in a Gay flick: "SKUFF 3: DOWNRIGHT WRONG DISC" with Jason Ridge.