Don, Thanks for the reply. Mother has already ordered the Jabsco pump. It appears that the main part of the inlet is 3", and I can cut off the 1 1/2" part and drill a larger hole with a hole saw if I need to. Bobby from Valdosta on the A/S list wrote that he uses a marine pump and it works great. So I may just adapt the 3" outlet to the 1 1/2" fitting.
Rick, The main advantage of the macerator pump is that it is a pump and does not depend on gravity to move the waste. It is possible to pump waste up to the vent stack on the roof of a building. And you can pump the waste for 100' or more. The one I put on my Squarestream will spray water for a considerable distance. The other advantage is that it uses a garden hose instead of the "stinky slinky." The hose is easier to wash out with the gray water, and is easier to handle without getting "it" on you.
In my parent's situation, they have a Coachmen trailer set up in their yard in Florida as a guest cottage. They bought it new about 3 years ago, but have given up pulling it. My father (who is 84) has been carrying the black water from the trailer to the toilet in the house in a 5 gallon bucket. The main purpose is to make it easier on him. It's not really practical to run a 3" sewer line out to the trailer, but running a 1" line back to the side of the septic tank won't be too much of a project. We're going down the first week of April sometime after the Ice Breaker Rally at the Top of Georgia, I'll add a post of how it turns out, and hopefully some pictures.