Just a couple of points. The issue with dumping black waste is that said waste is associated with blue chems which destroy septic tanks bio. The simple answer is to use organic fluids in the cassette. Personally we have been using them for many years now., 20+ at least.
Re the sites open for 6 months? That is down to the council licencing system as I understand it not the owners. The traditional holiday period in Scotland has until very recently been Easter which alone is a moving target, through to mid October taking in the mid term holidays in England. Out with those times was uneconomic. It takes time for people to adapt to major changes and remember they need time to repair and renovate. Not to mention have time off to recharge.
Then there is the little matter of cheap abroad destinations opening up again so is the pressure already heading south?
B2