I never mentioned I wanted to dump gray on the beach.  If I wanted to do that then why would I even ask about dumping gray in the first place?  Use your head guys.
Anyway, there are dump stations in the parking lots of these beach campgrounds but some sites are a considerable distance from the dump stations so I need a way to transport the gray across the sand.  Some ideas I came up with are...
1)  Use the 35 gallon tote we normally use for regular campgrounds.  Only issue is that we wouldn't be able to get the truck close to the sewer line on the camper and wouldn't be able to pull the tote across the sand to the truck.  We'd have to fill the tote and then tie a rope between the tote and truck in order to pull it out into the open where we'd undo the rope and then attach the tote to the ball as we normally would and tow it to the dump station.  This works but I'm afraid of damage to the tote once we hit some deep ruts left in the sand by previous vehicles.  It can get pretty bouncy.
2)  Pretty much the same as option 1 but make some kind of flat bottom sled to put under the tote while towing it across the sand so that it doesn't dig into the sand while towing.  In essence, the tote would kind of be floating on top of the sand.
3)  Keep the tote in the bed of the truck and get a macerator pump to pump the gray into the tote on the truck. Then drive to the dump station and empty the gray from the bed of the truck with a long stinky slinky.  
Are there any other ideas?  I kind of like option 3 but I don't know how loud a macerator pump is and how quickly it would pump 35 gallons of gray water.  The run would probably be about 15' across the sand and then up into the bed of the truck.