I've just left the strings to soak in some (purple) methylated spirits. Didn't have any pipes, so coiled them up in the bottom of an empty large 5 litre water bottle. Took a bit of persusion to get the strings to lie flat at the bottom, but will cut them the bottle up if I can't get them out later. Did try using a large biscuit tin, but it wasn't quite water tight, and the meths leaked out!!
Edit: 24 hours later, don't use a bottle unless you can cut it up afterwards, the strings didn't want to leave by the normal entrance and had to be cut out of the bottle. As I had only partly straightened the ends, they managed to get completely tangled up. Dried them with paper towel, and re-fitted them - they do feel a lot cleaner, but not sure whether they sound any different. PS - meths probably would ruin the biscuits, but biscuits don't last long in my house!!