I can't imagine how unsanitary the whole area would soon become if everyone dumped like this. The splashing alone would contaminate the underside of your own rig, plus anything within a wide area. I have never seen this done and to think of it is disgusting. It only takes a few minutes to connect and disconnect the hose.
But I have seen many disgusting things people do in campgrounds. Kids peeing in the playground, dogs pooping and owners don't bother to pick it up etc. And what they do in restrooms is totally disgusting. I could post pictures but I'm sure it would get flagged as inappropriate.
People are pigs... .SOME people, most are really great. No respect for anyone else, you see it in so many ways.. very sad.
2011 Toyota Tundra double cab