We all will have an accident at sometime when filling our portable totes. We're tired, maybe not paying attention or missing a step when disconnecting or reconnecting the sewer hose. Maybe we forget to close the valve. In any case the goal is not to spill anything, especially blackwater. I started placing a small plastic bucket or pan under the drain port. Even if you forget to close the valve, the bucket will give you enough time to react. Sure you have a nasty bucket to take to the dump station, empty, wash and sanitize, but it's heck of a lot better than cleaning up underneath your camper.You can't do a good clean up unless you move your camper.
We have found using newspaper to soak up the mess is easier than using kitty litter. Kitty litter tends to make mud and it's harder to clean the area.
We love to travel in our 2021 Coachmen Beyond van about half of the year. Join us, if you will, to see where our adventures take us.