Well i actually did this... let me just tell you what I did. Me and a friend of mine took a water hose and and a bottle of dawn dish washing soap, filled the tank all the way full, let it set for two or three hours then drained it. Then we left it empty for a week. To test and see if their was anything left in the tank. We hooked some wire to an electric fencer, got a 100 ft extension chord, plugged it in and went inside to see what happened, it kept a flame going and burnt most of the residue out. We left it for an hour and a half. Then we filled the tank with water and soap two more times. The second time we filled it, we filled it completely, then dumped about half of it out. Then we to a reciprocating saw (sawsall) and cut out the top for the doors that we had marked out....After we had those cuts made, we dumped the rest of the water and finished cutting out the doors. When the doors where finished, and the tank was dry (the next week) we got some wood and built a huge fire in the tank to get all the smell and left over residue out....I use the tank all the time, and works great.....hope this helps.