Our Minnie came with the AquaMagic 4 toilet, which is probably the older brother of the model 5. The space below the flush valve wasn't a simple pipe, but a large space that the "stuff" dropped through on it's way down to the pipe that went to the black tank. Plenty of brown stains collected on the walls of this space over time. As Old-Biscuit says, everything below the flush valve is open to the black tank, so any kind of leak results in a awful odor. Our toilet developed a very bad odor leak last year. I think something broke or cracked inside, but I wasn't about to take it apart with all that stuff inside.
After a lot of online research and reading product reviews, I finally settled on the
AquaMagic Style II. I liked this toilet because it has a simple straight drop pipe below the flush valve, the water flush system does not go through a space that is open to the black tank and the flush ball has an O-ring shaft seal - no cables going who knows where. In the link above, click on the Parts link to see an exploded view.
We have used this toilet on our last two trips with no issues.
2003 Winnebago Minnie 24F - Ford E-450🙂