locomotive sanding facilities - how do they work

this is a topic similar to my question about fueling facilities. I would like to know how modern railroads get the sand from the covered hoppers into the sanding towers? is the sand stored some place between the hopper and the sanding towers and how is the sand kept dry. My modeling era is the last 30 or so years right up to present with high horsepower locomotives and stack trains.

Thank you for your answers in advance.

Ted

Not sure if you’ve already seen these but here’s a little light reading Ted…
http://www.mcilvainecompany.com/Decision_Tree/subscriber/Tree/DescriptionTextLinks/Filtered%20exhaust.pdf
http://www.macton.com/rail_equipment/locomotive-sanding.htm
Not that I model the Modern Age, but I did find it interesting that improvements in sanding technology was slow to move with the times.
Cheers, the Bear.

Thank you Jabear. the pictures on the macton website were very good.