Where to start????
I think (and I am sure that an expert will contradict me, but here is my thought anyway...) that ARVs are built with large holding tanks, usually about 50 gallons, so that they are not looking for somewhere to dump every day. Most RV tanks will last a family for several days without needing to be emptied. A cassette would need to be emptied pretty much every day to stop it filling up and I do not know of any RV owners that would swap their tank for a cassette, with all the discussions that go on, it really is not a big deal, to be honest, most of the chit chat is about "which method" to use.
I certainly would rather experiment with methods than having to do the Thetford Walk every morning



I hope this explains it mate
Keith