Somewhere (not sure if here or not as I couldn't find the thread) I read a tip to try when washing long pieces of fabric. The tip was to safety pin (rust resistant) the selvedges together down the length of the fabric.
Well, it's a great tip! I just washed a 4-yard piece and it came out beautiful! Very few wrinkles and no twisted up mess! I'm going to wash all of my long yardage this way from now on. If you haven't tried it, give it a shot. I bet you will be pleasantly surprised! :D