Thank you, Wet_Boots. I've just been browsing the site and came upon the detailed description of the various cross-connection prevention devices here:
http://www.sprinklerwarehouse.com/articles.asp?id=187
I'll let my neighbor know about the recommended upgrade. I thought I was going over there to plug in his timer or replace a solenoid. Now I know a lot more about irrigation than I ever dreamed I would. Not quitting the day job, yet, though.
Thank you!
SD