Stayed last night (Sunday) and it was all very straightforward .
Arrived 17.30 and parked 8m Hobby in a single bay with the rear axles on a concrete area, first row in from the river. I called the control from the pay station and asked if that set up was ok by them and there were no objections. The bays along the riverside were taken but there's only one that would have suited us and that was in a poor state so we will go for the main parking area in future. Left today just before 14.00 and the grand total was £7.50. As for emptying a cassette, I saw no way of doing it although the disabled loo outside the cafe was locked with a notice saying the loos were available only when the cafe was open but I wouldn't be happy if I was tucking in to my full english and someone trots in with a container full of hobgoblins.
I will do a s someone suggested and send the council a valedictory email. I might even try flying a kite with regard to having access to an inspection cover or something to tip off the loo.
Cheers
H