Tea bags aren't washed when they're used in quilts so why would coffee filters need to be? Let it dry and brush the grounds off. You could always use dye or paint, instead of coffee, to color them if you want 'clean'. Several artists do that. Dryer sheets are also used, again painted, dyed, stamped, or otherwise colored...even dryer
lint is used. It's a whole different world on the art quilting side of the street.
