I use a small galvanized horse watering tank (about 25 gallons) set on some bricks. Poured in a bunch of cans of Drano and (slowly!) filled it 2/3 of the way with cold water (run the hose from remote control....you don't want to get splashed with the stuff!). I keep it covered with a piece of sheet steel when not in use. It works pretty well cold, but it is set high enough to slide a coleman stove under it. With warm-to-hot water it is incredible. Make sure you have a way to dispose of the solution when the time comes to replace it. Mine has lasted a couple years with occasional use.
Disclaimer: Drano is Sodium Hydroxide, commonly known as Caustic Soda or Lye. It's nasty stuff! When it comes in contact with skin, it will make you wish it were only battery acid. Don't let anything organic (e.g. plastic, rubber) or aluminum come in contact with it. Only use with steel or cast iron. Remove all bearing materials. Be careful!
