To unlock this you must clean a map quite alot, almost at 100%. This goes for any stain on floor or walls, bullet holes, body parts and trash items must be incenerated, moped up and removed. Buckets with blood or dirt in must be incenerated too. Wet floor signs must be placed if needed too and crates and barrels must be stacked properly and at right location. Once you've done all of this you can checkout and the achievement will unlock.