I like the idea of making a test quilt sandwich, marking it, washing it the way you washed the quilt, then trying various things to get the marks out. (The test quilt needs to have the same fabrics as the real quilt.)
Here is a link to one thing I had never heard of that gets good reviews:
http://www.amazon.com/Shout-Wipes-12...dp/B000FE0PC4/