Rad drain

I'm trying to drain the coolant form a 93 Caracan but the drain no longer drains. Only a few drops come out of it. It's the original rad. Can someone confirm that its about 1/2 turn to fully open it (I can't remember)

Two years ago it worked fine. I guess there is a thick layer of deposits at the bottom of the rad.
I was thinking of connecting a hose to the drain and backflushing but it's hard to get access to the drain.

Anu suggestions?

Turn the drain valve all the way out and don’t forget to remove the radiator cap