If you do not prewash, it's probably safe to wash the finished quilt in a *large* washing machine (one that uses lots of water) with Synthrapol. The bleeds are kept suspended in the water (and diluted because there is lots of water) so the loose dye particles are rinsed away instead of settling into other fabrics. I would probably use the largest front loader at a laundromat for this (as I have a domestic front loader, which doesn't use enough water for Synthrapol to work well).