Used to do the soap and water thing - until I found this stuff. It looks pricey, but since you only need 3 or 4 drops on a gun cleaning patch, it is actually pretty inexpensive. I've wiped down a line that was just cleaned with the soap and water treatment, and actually removed more dirt. It doesn't gum up the line, and wears off after a long day of fishing, so you have to re-apply it at the end of the day. Takes me less than two minutes to do the whole line.
A side benefit of this product is that you'll feel that the line is significantly slicker, and shoots better than new. It uses teflon instead of silicone, and will not harm your line. It seems to make the line float better as well. I've been using it for 3 years now, and it really does work well.
This product is called Zip Cast, and can be found here:
http://flyreeldots.com/