I’ve always heard of the girl pulling a train. But it seems like kind of a dated term since gang-bang is so frequently used now, and extended to other meanings (or perhaps it had other meanings first).
I didn’t like It. About half of King’s books don’t appeal to me. Considering the total volume and individual sizes, that’s still an impressive record.
In IT I recall twice Pennywise being introduced as Robert - or Bob - Gray:
When introducing himself to Georgie in the beginning and when a certain old lady (trying to keep it spolier-free, here) tells Bev who carved some furniture in that house.
[speaking as a female] To me ‘a girl pulling a train’ sounds more consensual than ‘gang bang’, perhaps it is the term ‘gang’ which tends to bring to mind a bunch of unruly young men out to be obnoxious with a side of violence.
But you are right, ‘pulling a train’ is the older term, haven’t really heard that in a fairly long time. Random check on youporn you find gangbang more than ‘pulling a train’, and a fair number of sex ‘on a train’ meaning the physical transportation item.