I stayed at a CC&C site in Surrey just off the A3 which has a large fishing lake earlier this year in the hot weather( remember!) An American motorhome, of medium size with air con etc, was pitched next to the water disposal point some 25 feet away. On the Sunday morning, as he was packing up, he opens the waste valve and pours the contents of the waste tank all over the pitch.
I think that there was a MH disposal point up by the office, so in my opinion, this was being purely lazy and arrogant. Surely they have room for a waste container to empty it properly.
Being a tent site as well I wonder what the next person thought.
Treat others as you would like to be treated yourself is a hard one to knock in my book.