Can't figure out how to loosen or tighten this tailpiece

[mystryda]

I've done a fair amount of household plumbing, but I cannot for the life of me figure out how to get this tailpiece looser or tighter.

The collar slides up and down on the tailpiece (see second pic how the collar can be slide up from the flange beneath) but it doesn't spin, even with one pair of channel locks on the collar and another on the flange. Help?

I bought the vanity/sink used on Craigslist.

Thanks in advance.

 

[Reach4]

I expect you will have to cut some wood to clear the nut.

You may need to replace that drain if the threads are messed up.