We used to do this with a barrel stove also. The oil tank was a 5gal bucket with the top cut out. This made pouring the used oil in the tank pretty easy from a drain pan. We would put the biggest stick of wood we could find or fit into the stove and let the oil drip onto it. One stick of wood would last a couple of days. I dont remember much ash, altho I am sure there was some. I guess when burning mostly oil there shouldnt be much ash to dispose of.