How to deal with grease on ball of receiver

I used a 4 inch PVC end cap with the screw end cap. It fit perfectly over the ball. I then had a cloth bag with draw strings I'd slip over the hitch and end cap, so if driving down the road the cap would not fly off. I also kept the cap and cloth bag over the hitch when detached from the truck and stowed away. Because the end cap did not have to "forced" over the ball, and because it was actually bigger than the ball, grease on the outside of the cap was never a problem. It always stayed inside the cap. If we were at a campground and I knew the truck was not moving (like a short week-end), I'd just put the cap over the ball without the bag.