The unit that I was referring to is evidently made by Sealand. It is item #500258 on the following page (the one at the bottom of the page):
That model has a 9 gallon holding tank that has an 1-1/2" outlet that can be hooked to a macerator pump.
There does seem to be quite a variety of different combinations of features in the marine category. I wonder how effective the manual pump units are. I would suppose that they would be quieter than electric units. The Blakes Lavac toilets are somewhat interesting in that most of them seem to be designed to have either a manual or electric pump mounted remote from the toilet itself. There is a Zenith head pump on the same page as the Lavac toilets that has the interesting feature of being able to work for the toilet as well as for pumping out the holding tank using a divertor valve. The pump does seem pretty expensive at $675 though. See the following page:
I wonder if marine toilet electric macerator pumps are designe to handle the extra riggors associated with using salt water to flush? It occurs to me to wonder how marine holding tanks get pumped completely dry if they are having to pump up? Do they have low pickup points in them? The general marine holding tanks that I saw on the site are either the flexible type or more or less rectangular units. Most RV tanks have sloping bottoms that are especially oriented toward gravity assisted dump. That does not seem to be a concern (or even a possibility) with the marine units. Do the flexible tanks shrink up when the are pumped out I wonder? Some of the holding tank prices are pretty good on this site too if you can live with one of the standard sizes. On the following page you can get a 40 gallon tank for $109.99 which seems like a pretty good price point to me.