definition

I was looking at an older site and came across the term "choo choo'. Definitely a term from the hobby. Does anyone know what it means?

We once upon a time referred to a lady who undertook to service a number of men sequentially as "pulling a train." Alcohol was often involved. Perhaps that was what was intended.

Yes that's it.

A serial gang bang, so to speak?

I thought it was like pulling a train also. However, in her accounts, she would refer to doing "choo choo" with only 1 client (the same one guy all the time). Thought it might be like fisting but not sure.