I pre-wash all my fabric. And if a quilt is to be used, I give it its first bath. I use Orvus Quilt Soap and follow the instructions for very delicate quilts which means the quilt goes into the tub.
The water turned brown which wasn't terribly surprising given that I've been carrying the quilt around for the last ten years. I rinsed it twice.
I used a sheet to gently lift the quilt from the bath, and as the weather was (unseasonably) warm I carried it to the deck table to dry, covering it with another sheet for protection. Night came too soon, so back indoors it came. It spent the night loosely folded and draped over my ironing board. I'd have to wait until it dried to see how my hand quilting stitches transformed as the batting shrunk.
In the morning I saw red instead.
The quilt was still damp so I ran another bath and added Synthrapol. I use it to remove excess dye from fabric I've hand dyed so fortunately I had it in the house. This product removes excess dye molecules that haven't formed a chemical bond with the fabric.
I can't recommend it highly enough as I am very happy to report that it worked.