Well Thanks for all the suggestions. I ended up dropping the tank without draining (I could only siphon so much). I will let you all know what I end up using for removing the plug.
Now I have to do decide what to do about my nasty clog. When I look in the tank I see a tube leading to a puck looking pickup. I really don't know how I am going to clean out all the crud from under the puck without cutting a hole in the tank and removing the pickup.
I am thinking that I just may block off the original pick-up tube and have a new bung brazed on. Any thougts or warning against that idea.
Unfortunately it is a wagon and no replacement tanks are available and my tank does not look that bad in or out.