I was under the impression that draining can be a bit of a ball ache, especially with a tank in the loft.
I also read that 8mm microbore can easily get blocked up, so changing one valve after draining could leave other pipes blocked.
Anyway, I bought some bungs and all the kit I need so I'll be doing it with a vacuum this weekend. Yes, I'll set up a GoPro so that we can have a laugh if the vacuum doesn't hold 😂