For rubber floor mats, I just set them on the ground, spray them with some properly diluted APC, give em a quick scrub with a brush, then blast them with the pressure washer. Then I pick em up, shake 'em off, set em back down and spray them with dressing and allow them to dry until I'm done with the interior giving them a light wipe down if needed. If your getting staining where you applied your APC, chances are very good that it's mixed to strong.
This method also works with super dirty rubber backed carpeted ones. Instead of the dressing, I give them a good sucking with the vacuum, a good wiping with a terry towel, a blow with the air gun then apply brush strokes to the carpet nap, and let them sun dry.