Dometic (formerly SeaLand Technology) claim that their VacuFlush can use "as little as" 1 pint of flush water has misled a lot of owners into believing that's all it needs. And as a conseqence, at least 75% of all marine toilet problems posted online are from VacuFlush owners, almost all of which are the result of too little water going through it to rinse bits of solid waste and TP out of the system.
Fwiw, VF was the toilet on my last two boats and I was a dealer for nearly 10 years...so I'm intimately acquainted it.
If you want to stay with a manual toilet, the Raritan PH SuperFlush
Raritan PH SuperFlush is top rated...Raritan's Fresh Head
Raritan Fresh Head is the ONLY manual toilet designed to use fresh water.
If you want the "pushbutton" convenience of an electric macerating toilet, the Raritan Marine Elegance, designed to use pressurized fresh water,
Raritan Marine_Elegance Promo.pdf is the top rated macerating electric toilet. The more basic Raritan SeaEra, a sea water toilet,
Raritan SeaEra Promo Sheet is top rated in its class.
Don't let the list prices of any of these scare you...they're all available for a lot less if you know where to shop.
--Peggie