I have been using the Crayola brand WASHABLE markers for years, and have never had a problem getting any of them washed out of my quilts.
With that said, I must add that I heavily starch my fabrics as I'm making my tops which provides an extra protective layer and even pencil marks easily wash out.
(I once marked an entire baby quilt with a dense wholecloth design in pencil, and all the marks washed away in the first washing.)
After my quilt is finished I
soak it in the washing machine with cool water for about 15 minutes, then drain all that water out of the machine.
I then run the quilt through a regular cycle with a mild detergent and warm water.
I usually use Orvus Paste
http://www.farmandfleet.com/products/062513-orvus_paste_soap.html
then rinse the quilt twice, just to be sure all the chemicals are out of it.
You may find this article informative about washing quilts in general:
http://www.fortunecity.com/victorian/magenta/14/id29.htm