Sometimes, a conduit run is too long or has too many bends even for fish tape. Or perhaps the bends are too sharp, or the conduit has a joint or connection where the fish tape gets stuck. An alternative method is needed to get the wire started for the pull. In these cases, a handful of paper towels1 can be tied to a lightweight cord at one end of the conduit, and a shop-vac hose can be placed under the other end. While not completely airtight, the conduit should provide enough of a seal to allow the shop-vac to pull the paper towel through the run, trailing the lightweight cord behind it.
The cord can then be tied to the bundle of wires in order to pull them through the conduit. If the pull is particularly difficult, it may be necessary to use the lightweight cord to run a heavier cord and then use the heavier cord to pull the wires through.
A bundle of wires is most easily pulled through conduit by folding over the end of the bundle so that it forms a loop and then wrapping electrical tape on about 6-12" of the bundle to hold it together. Tie the end of the cord or the fish tape to the loop formed and pull it back through the way it went in. Wire pulling lubricant may be necessary. This is usually a two-person job, one to pull the fish tape from the far end and one to help feed the wire through without kinking or tangling on the other end.
Always run conduit a little too big for the number of wires it needs to hold, it may be necessary in the future to add more wires. This can usually be accomplished by using one of the original wires like fish tape to pull the new wires through. If you don't mind the clutter, you could also simply run extra wires in the bundle to begin with.
1. Transitional Man says plastic sandwich bags work better than paper towels.