Having just come back from the nene,grt ouse and cam area, I found that when taking on water,that it was difficult to get the thing to unscrew again, when we filled at earith, someone had cut their hose and left the end still screwed on, but when I went to unscrew it , it came off very easily, but after I filled up, I then couldnt inscrew mine, and had to cut my hose, and then use the one that was left on earlier to renew mine. Exactly the same scenario happened at cambridge jesus lock,although , I was able to to get mine off again, and this time used the screw left there as it was a better silver screw and was able to use there jubillee clip.So I summise that after filling up the thing must swell for a bit afterwards, but then shrink to original size making it easier to then undo. Never noticed this anywhere before,cant be a case of doing up too tight as after a while it is then easy to unscrew. Just weird and an observation if anyone has the same problem..