I use denatured alcohol to clean my strings.
I always have one complete set of strings laying in a PVC tube filled with denatured alcohol. So when my strings are loosing their bite, I just swap the ones in the tube and the ones on my bass. Works like a charm
Everything you need is an airtight container, so that the alcohol doesn't evaporate.
There used to be a nifty guide to making one here:
http://www.tunemybass.com/strings/ba...ning_tube.html
You could try the way back machine at
http://www.archive.org to see the page. You won't get the pics, but you can at least read the guide. Any good hardware store should be able to help you find the necessary supplies for making one.