Bought a small home fire extinguisher (dry chemical), and had to use it for a small stove fire. The needle is in the middle of 'empty', (not all the way, but it appears that the fire extinguisher is of the one time use type, and is non-rechargeable) and the label says to discard if the needle points to empty.
I don't just want to chuck a fairly large metal tank into the weekly trash, even fully discharged does that present a danger? Or, is that the proper method?