Don't use Retayne as it sets the dye! You use that on yardage before you cut.
Synthrapol keeps the dye suspended in the water rather than being deposited on the fabric.
Use cool or cold water, and lots of it (i.e. don't use a front loader or high efficiency top loader). Don't agitate. You can also wash it in the bath tub. Put a sheet down, then the quilt. after swishing everything around and draining, you can use the sheet to lift the quilt out so you don't put strain on it. if you have the room, dry flat.