Thank you for the tip, I have tried a variety of pen. Get some waste aida or evenweave, scribble on it and leave it to dry, then wash and see which works best.
They make a product now that essentially does the same thing, but doesn't leave behind pencil marks. It's almost like a fishing line, except it's red. It will pull out easily after being stitched over. I've found that some patterns have light colors that show pencil marks through the stitches.