Better yet, use the IPA found in home improvement, paint or hardware stores sold as "alcohol", designed for use as shellac thinner. It's 100% isopropyl alcohol and available in pint or gallon cans. Old toothbrushes work well for scrubbing and you can use floss to get underneath components on the other side (just kidding, just kidding!). For larger boards, fingernail brushes work well. Just remember that the brushes will cause splatter, so wear eye protection and keep your bench clear of things that you don't want splattered.
More dangerous because of explosion/fire and inhalation hazards, either lacquer thinner or acetone work much faster for non-water soluable fluxes. Two runs with the stronger solvents and a final rinse with IPA will leave your board clean as a whistle. Overall, I'd suggest doing it outside on the driveway just to be safer all around.
However, remember that flux removal, for the most part, is a cosmetic thing. Flux at room temperature is inactive and non-conductive, and as long as your circuit board is installed where you can't see the solder side, I wouldn't mess with it.
Dean