Pulling aid for cables in a conduit: cotton, cord & vacuum cleaner
Take a small cotton ball that just fits into the empty tube. Tie a thin, tear-resistant string to it (I use a kite string). Now put the cotton in one end of the empty pipe and suck on the other end with a vacuum cleaner now on the cotton ball. Now attach the cable to be pulled to the cord and pull it back.
It is best to wrap the cable beginning with insulating tape, so that no edges or corners look out and use some grease as a lubricant.
