Thats been ongoing for a while- I had to look at a boats toilet system and clarify that it did discharge into holding tanks many months ago.
I am not sure about the 'illegal' bit though as sea toilets are allowed on the River Great Ouse. Certainly I agree it is not a very good idea for many static boats to be discharging into a marina though.
I had no idea about the composting loo's though.Interesting as I fitted one a while ago- surely they can only insist you dispose of waste elsewhere?