It's a poly tank with the inlet on the top. It looks like it's threaded, though I didn't measure it. I want to moving to vacuflush for a few reasons.
1) Holding tank capacity: The electric flush uses raw water and far too much of it. I have a 30 gallon holding tank that I need to empty more frequently than I would like.
2) Odor: The electric flush uses raw water. I only use the boat on weekends. The saltwater leaves an odor in the head after baking in the heat for a week.
3) Noise: The electric flush is loud
I'm surprised moving to a vacuflush is considered a move backwards. I really haven't seen many new boats sold with electric flush in recent years.
The platform the head is located on has limited space, as a result, I am limited in the models I can install.
As Peggie said, an electric freshwater toilet can address all these. The amount of water you use can vary all the way down to "hardly any" (via the "flush" control panel), fresh water flush doesn't have the same kind of odor issues as would raw water, and there's only one pump action going on (macerate/discharge) rather than two (bringing in raw water being the second).
One issue might be about your toilet discharge hose, and how that runs to the holding tank. If it's a downhill run, after waste zooms up and over the first loop just after the joker valve, then that hose will mostly drain itself with each flush and you'd probably not have to worry too much about permeation.
OTOH, if you've got a bit of uphill in it somewhere, any "belly" in that line might mean more rigorous flushing (so standing waste in the hose is actually just fresh flush water) and maybe eventually it'll need replacement due to permeation. You could address this with a PVC run instead of flexible hose. Or you could just plan on replacing that one hose, maybe 5/8/10/15?? years down the pike.
But Peggie says Raritan's SaniFlex has never permeated; I'm gonna test that.
Actually, I at first thought to make that run on our boat (almost all "belly") out of PVC, but it would be slightly complicated and I've not worked with PVC before... so I chose to defer that learning curve until after the SaniFlex test... in 5/8/10/15? years or so.
From my experience the Jabsco Quiet Flush isn’t. The Raritan ME is pretty quiet and part prices aren’t stratospheric either. Before you lock yourself into Vacuflush price out the spare parts. They control the distribution so the prices stay high.
Our QF got much louder when the macerator/pump assembly seals started to fail... at about the 10-12 year mark, IIRC. Replacing the macerator/pump motor assembly, relatively inexpensive, 10 minute change, brought the noise level back down.
Given I've not heard a Marine Elegance, I can't really compare... but I'd guess IF the QF toilet base is a direct replacement for Shrew's existing Jabsco raw water model, it'd MAYBE be a much easier swap than maybe switching to the ME. That's really the only reason I mention it as an option, given how much everyone loves the MEs.
Our QF is MUCH quieter than the VacuFlush we had in our previous boat!
-Chris