I'll find out tomorrow as I don't really have any plans to go out today ...
clarkie34, It didn't need any force to open the butterfly valve ... It just requires a bit of pressure to open it ..
I think next time I'm going to remove it completely and give it an even better clean ... but for now that's done the trick!
I should have taken some pics of the cloth after I'd finished cleaning ... It was almost completely black by the end ..