Yet another use for duct tape: when trying to draw a new cable into a bottleneck using the old cable as the draw, linking the two together almost always creates a lump that can hang up if the passage is really tight. I have run up against this many times in the past.

Instead, just place the two cables end to end on a piece of duct tape, then roll the tape tightly around them. This creates a non-bulging join and the tape will hold the cables surprisingly well. I have been able to successfully pull several using this trick. Duct tape is a truly magical thing.