For those who are wrestling with this, I spent some time on the telephone with Sealand, both Factory and one of their third party installers that they referred me to. Their products all have top feed waste removal fittings, with tubes that go to the bottom. when you look at their diagrams, you probably wind up with less in the bottom with their tubes than you would with a bottom discharge because of run back from the hose, etc. they say it works fine, and are standard in SeaRay, etc, which I have always thought of as a pretty well built stinkpot. They confirmed no need for macerator, that the action of the wilcox pump and joker valve pretty much chops everything up. The installer said that there was one grand banks that he knew of that had the sweet tank systme (pumping oxygen to the bottom of the holding tank, sort of like keeping a fish tank oxygenated keeps certain bacteria from growing) and that it worked well.
Now to do the deed.