What products and process should be used to clean a climbing rope when it gets sufficiently dirty? How would I remove as much dirt and grime as possible without negatively affecting the strength or lifespan of the rope?
All the major climbing sites agree on the two options for cleaning, and the subsequent drying:
Wash in cool water (less than 30°C) and use a mild detergent, either in a bath, or in the shower. Some people place it in the shower while they wash. Gentle brushing can help remove grit or sand, but be wary of abrading the strands.
To machine wash, pop the rope in a pillowcase and use a ‘delicate wash’. Some recommend daisy-chaining the rope first to hero keep it tangle free.
Generally treating a rope like a delicate wool article is a handy rule of thumb.
Once washed, hang it indoors, in a dark, cool area, and allow it to dry naturally.
Even though some people do wash their ropes in washing machines (inside a bag), I would never do that myself. And REI does not seem to recommend that either. I have myself washed a rope by hand in a bathtub with a special rope washing detergent (e.g. one from Tendon), and the results were great. According to REI, a mild soap could be used for this purpose as well, but I guess I just don't like taking risks with life saving equipment.
For even better results you might want to try a special rope washing brush, e.g. one from Beal. It might also save a bit of time. As I have done all my washing with hands only, I cannot tell how much better/easier it would be. My rope was clean enough after just swirling it around in the bathtub, and running it through the hands a few times.
You should make sure not to use too hot watter (max 40 degrees, which is about the body temperature). After washing the rope, you should dry it unfolded in a warm dry spot without direct sunlight, and also not directly next to heaters either.
The final advice would be not to wait with rope washing too long. Climbing on a rope with no dirt in it is not only nicer, but it also prolongs the life of your rope. Dirt parts rubbing against threads within the rope do weaken them.
If you want to get your ropes clean in a hurry, use a rope brush:
This is the result after pulling your rope through one of these brushes twice:
Fill your tub with cool to luke warm water, then make the water a little soapy using a bar of soap and flake your rope in it to soak for a while. After your rope is drenched, use you hands to clean off any extra soil, and then start pulling your rope through the brush. Each pull will produce a cloud of dirt in the water, and the water will just get blacker and blacker as you go.
I recommend getting help with pulling the rope. Your arms get tired in a hurry when you're doing it by yourself.