There are washable pens for quilting. I use frixion pens (which disappear with heat). You can also get weird soap type pens that wash out.
Pros Cons
Washable wash out, but they fade quite quickly so you have to quilt within the month of using really.
Frixion disappear with an iron, but the lines have been known to show a little if the piece is stored somewhere very cold. Also the best colours are black and blue. They don't fade over time.
Soap type things, wash out but give quite thick lines, may not show well on lighter fabrics.