Here’s a Crafty Rope Trick (CRT) for the local crag - use someone else’s rope to set up your toprope.
Scenario: you’re waiting at the base of a popular route at for the previous party to finish their climb. While you’re keen to try the pitch, it’s rated at the upper end of your comfort level for leading, and you’d really prefer to climb it on top rope. Here’s how you can use the rope from the previous party to set up your own top rope.
Before the previous team has pulled the rope through the anchors, ask them if you can do the following trick. Pull out your roll of athletic tape (which should be in every rock climber’s backpack), and tape one end of your rope directly to one end of the other team’s rope that’s running up and then down through the anchor. This connects the end of your rope butted up to the other, with no knot that would otherwise get caught in the anchor. Tape it generously and tight, with 3-4 inches of tape on either side where the rope ends butt up against each other. Now, the previous climbing team can pull their rope through the anchor. If all goes well, it also pulls your rope up, through the anchor, and down to the ground. Remove the tape from the two ropes, and you’re all set up to top rope. Slick!
I first saw this Crafty Rope Trick in a rock gym, when the course setter was replacing a worn out rope. I thought he was going to have to climb the route and thread the new rope through the anchors, but nope, he stayed on the ground the entire time and use the old rope to pull the new one through the chains. Very crafty!
Etiquette note: After the first person on your team gets to the top, it’s generally best if they make an anchor with their own gear and rerig the rope to run through it. This way, you’re not toproping directly through the fixed anchors and thus putting unnecessary wear on this gear. (This practice can change according to the climbing area and the type of hardware in use, so ask the locals if you’re unsure.)
1 - Place the rope ends butted up together. Try to get the rope ends lined exactly, so there's no little bump in the final tape wrap that could get hung up.
2 - Start wrapping athletic tape around the ropes, 3-4 inches from the end.
3 - Keep wrapping, overlapping the tape edges, and giving a few extra wraps where the rope ends meet.
(Yes, I swapped the ropes left/right for this photo, but I bet you can follow along . . .)
4 - Give a few squeezes to the tape when you're done. Leave a cm of tape of so left over and fold it back so you can easily unwrap it. The final length of tape should be about a hand span, or 6 inches.
5 - Done! Now, when you pull one rope, in this case green . . .
. . .the taped ends should pass through the chains . . .
and all through! Keep pulling green, and then you're ready to toprope on blue.