Do not use RainX on vinyl windows. It will lead to cracking/crazing and discoloration. It's made for glass, not vinyl.
There are treatments for vinyl windows (we sell one, but others do too). It's more designed to keep the vinyl clear than to help water run off, though.
Please make sure that any chemical you put on your clear vinyl is specifically designed for that.
Mild soap (liquid dish, not powdered detergent) and a soft cloth are always useful.