Another way they send leader through conduit is compressed air, connected to a feathered dart like a blow gun.
When building my shop, I ran three 2" conduit runs from my house basement, ~40 out to my shop. To run my mason's line for pulling wire, cable, etc. I attached a shop vac to one end of a run in the basement, took a plastic shopping bag and tied the line around the center, turned on the vac, stuffed the bag into the shop side and it sucked it right through to the basement. It worked pretty well.