Hi, You guys have helped me a couple of times now so that I have been able to do simple plumbing jobs myself, and I'm hoping you can do it again. The ballcock in my loft cold water tank needs changing - when filling the tank the old one sometimes makes a terrible vibration noise that echoes through the house. I have the new unit and it looks extremely easy to fit it, but my problem is removing the old one. I expected to find copper pipe for the mains cold water into the tank, but instead it is a flexible black pipe (HDPE?). I think I would know what to do if I found a regular copper fitting, but I'm not quite sure how to treat the connector on the end of the flexible pipe. I have posted photos of the feed pipe and also the existing ballcock fitting inside the tank via the link below. Should I loosen the large part that is connected to the flexible pipe? I don't want to mess anything up and end up with a leaky feed pipe. Thanks so much as usual.
Photos of feed pipe and inside tank: