I went out a couple hours ago and bought this. It is 15 gallons, and has a 1/2" npt bung welded to the bottom. I took some 1/2" street 90's and a 1/4 turn ball valve and did away with the hose and nozzle. I will just use gravity for now. If I find that it does not work out, I will try some of the other suggestions. This tank is steel, so I will likely send it to my galvanizer and have it hot dipped.
Longshot,
We just use a Tide bottle like this and carry it with us on the mule.