I got the chuck key for my lathe’s tailstock and stuck it in the hole in the side of the valve. I then put the hole thing in my vise with the soft jaws, grabbing it by the valve body. I grabbed the tank with a spanish windless knot and used a two by four to get the leverage. You could also use a pin spanner, but you will need to find a way to securely mount the tank and twist HARD. This thing is on there!!
use a adjustable oil filter wrench to hold the tank