The deck I have is made of treated lumber. Previously, before staining, I sanded down the spots where sap had bled through and hardened. Naturally, they came through again. I'm about to redo the stain again, does anyone else know what to do before sanding them off? If they're just going to come through again, do I even need to sand them? (They really gum up the sandpaper and it has to be replaced every 2 seconds.) Please help. Thanks!