Best way to clean gas tank

I was searching for answers as well on that topic this summer although did not talk to anyone in the business ( whoever that would be ) that could have provided the perfect answer to the mess I was dealing with. So in this case it was an old grain truck that had a behind the seat mounted gas tank and found out after draining it while in place of the very old gas and pouring in some new gas, crap came through the fuel line plugging the filter but also some of it went right through the filter and into the carb totally plugging it when I got it running, it was a god awful chain reaction mess. So I knew I had to remove the gas tank after I emptied it almost out and when I poured what was left out of it, it was like a dark brown tar and even gas could hardly remove it from surfaces such as inside the fuel filter canister. I can only speculate that it was a combination of other fuel components along with dyed farm fuel that was left behind over the years as the volatile components of the fuel evaporated. What I tried was gun wash for cleaning painting equipment or another words its a lower grade of lacquer thinner. Although it wasn't probably the ideal product it doesn't ruin steel and I would put a solution of that in and then rock the tank around to wash down the inside and then leave it sit for a while with the solution soaking in the bottom of the tank where the most crap was. I did this over and over and used lots of product and finally it came out almost clear. I bought the product by the 18.9 liter pail. The tank was not rusted through as that would be an entirely different ordeal and no doubt sourcing a new fuel tank if possible in your case.

I had thought of getting someone to steam it out but wondered if this crap would actually bake on, I just wasn't sure so decided to try the chemical route at first and imagine using actual carb cleaner would be ideal but that would be insanely expensive for the volumes I was using.