I found plenty of info online about how to clean the brush, water tank, and hose, but nothing about how to clean the top part of the water tank with the big grey dial that snaps onto the top of the water tank. It is collecting fuzzy gunk on either side of the dial and under the dial. All in places where I can't reach with anything but a long thin wire, but can't pull it out. Tried submerging it and soaking it for hours to loosen it up, no luck. There are 2 screws on the underside, but they don't release anything. Anyone have any suggestions?

Water Heaters - Bissell - Pro Heat 2x Select Pet Upright Deep Cleaner