Is it OK to take a piece of string and slip the conduit pieces you are putting together onto it before you assemble them? I was thinking that doing this would be easier than trying to fish or feed a guide-string through the conduit, or simply pulling the wires through it without a guide-string to help with the process...
You have to assemble it first, before wires, but putting the string in as you put it together is fine.
300.18 Raceway Installations
(A) Complete Runs. Raceways, other than busways or exposed raceways having hinged or removable covers, shall be installed complete between outlet, junction, or splicing points prior to the installation of conductors.