Grey water disposal with no sewer connection

Rolling portable waste tanks will not work for him. He stated that they are often higher than the one pictured. If he used a portable waste tank, then he would need a longer hose and then would have to lift it up. It might would take two people to do it also. Only way I can see is using a container that you can carry (or multiple containers on a cart) and lift to dump. When we had our pop up, we used those blue water totes for the gray water in the beginning. We used a sewer cap that had a hose pipe connection and would use a short piece of hose to let the gray water drain into the container. We had a couple of containers and you would have to keep an eye on them. When they were full, they would weigh a little less than 50lbs. Don't fill them all the way to make them more manageable. But they sell collapsible carts you can probably get a couple of 5 gallon water totes in.

Here's a good video about getting water while dry camping, but you can use a similar cart/container setup.