disassemble

Hi, I'm trying to remove the cartridge on this exposed shower mixer, but I can't for the life of me figure out what comes off next. I've removed the flow control handle and the little grub screw inside. I'm thinking I need to unscrew the outer chrome ring where the flow handle was connected...

I want to remove a swan neck fitting from the top of a cast iron soil stack which is about 4"/100 mm diameter. This piece attaches to the vertical stack with a lead-sealed socket joint (see sketch). How can I dismantle this joint? I don't want to damage any of the main vertical pipe, including...