Is yours 'numero due'-free?

I seem to come accross a number of folks who only ever stay on sites with a toilet block and, with that facility at hand, will not use their 'vans toilet for, ahem, number twos. The main reason seems to be squeamishness about the emptying part, but I thought that was the beauty of Thetford casette toilets, in that it was all contained and all you had to do was tip the contents away at the elsan point?