I suppose you should turn it until it begins to leak, then put a hose on it.
I had to use a 19mm deep socket with a pipe on the end. I just let it leak out on the ground. As I put a pint of water pump lube/ antifreeze restorer in mine on a yarly basis, the fluid was entirely clear, rust free and clean-looking after three years.
You will need to really tighten it. Mine leaked a bit after the engine heated up a bit. I'd start the engine with the car still on a jackstand, and make sure it was not leaking.
Hope this helps.
There is a place where you can put a tube on the radiator drain as well.
Semibodacious Transmogrifications a Specialty
1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)
"Time flies like and arrow, yet fruit flies like a banana"