The choice of bog type can get complicated. According to
https://www.dometic.com/en-us/us/products/hygiene-and-sanitation/sanitation/rv-toilet-buying-guide
there are five types:
Gravity flush – this is the most traditional toilet; tried and tested in RVs for decades. It uses the simplest method of flushing – bowl contents drop directly into a large holding tank – ensuring reliable, straightforward performance. The gravity-flush toilet must be installed directly over the waste holding tank.
Macerating flush – motor-powered blades macerate waste into viscous slurry before the waste goes into a large holding tank. This flushing technology allows the toilet and waste holding tank to be positioned apart from each other. As a result of maceration, holding tank effluent is more fluid. This reduces “mounding” of waste while also making discharge from the tank easier and more thorough.
Vacuum flush – bowl contents are powerfully pulled from the toilet bowl through a stored vacuum vessel and macerating vacuum pump, and then pumped to a large holding tank. Like macerating toilets, this flushing technology also allows the toilet and waste holding tank to be positioned apart from each other. This allows a vacuum toilet to be located virtually anywhere in a motorhome.
Cassette – primarily designed for caravans and campervans, this toilet technology provides a compact toilet bowl that’s permanently installed over a small, removable “cassette-style” waste tank. When flushed, the bowl contents drop directly into the waste tank. When the waste tank is full, it is manually removed through a service door and emptied into a standard toilet or other waste disposal station, then re-installed under the toilet bowl.
Portable – popular in small campervans and also for tent camping, portable toilets are composed of a lightweight plastic toilet bowl and small waste tank. When the tank is full, you remove the lower tank from the upper seat and bowl, empty it into a standard toilet or other waste disposal station, then re-connect it with the toilet bowl.
If you are new to all of this, learning how to clean and maintain whatever type you get is important.
We’re buying a tow-behind next year, and have decided on a cassette. We’ve agreed to a “pee only” rule, and use roadside or campground facilities for solid waste.