IIRC, a water trough would be 2-3,000' long, and the tender would have a water scoop that would be lowered while passing over the trough, and lifted(hopefully) before the end of the trough. The scoop would lead into a pipe that would be high enough in the tender tank, that the water would not drain back out.
I believe that the minimum speed for taking water on the fly was about 30-40mph to have enough force to get the water all the way up the pipe.
Doug
