I'm a pretty handy guy, but this nonsense has got me stumped.

I'm changing out an old fluidmaster from my tank for a new one. The
damn plastic nut will not loosen (yes, I know how to loosen a nut,
duh). When I try to loosen it, the fluidmaster body and the braided
hose turn also. Trying to hold the fluidmaster body in place is
impossible because the bottom portion of the body 'ratchets' and does
not bottom out.
How do I got this thing off?