I too am curious about what you saw.

It's just hard to imagine how, if it was not a cloud of vapor, a real liquid stream would be visible that far away -- and moreover, how a plane could be putting out so much liquid to make it visible that far away? If only we could have a picture or a picture similar to what you were seeing? One stream, you say?

Is it possible that a reflection or refraction of the sun at a certain angle into a vapor trail made it look like liquid?