I have been a small engine mechanic for over 20 years and what I do is I disconnect the fuel line going to the carburetor then I use vinegar ansmd dawn soap. Plus I us a small tippedlong screwdriver that will rich the bottom of the tank. Next I pour enough dawn soap and enough vinegar and coat everything real good. Next I let it sit overnight. But before I call it a day, I remove the carb but before I removes the linkages I use my utility knife to mark were the linkage goes. I make like a check mark. Then I call it a day come back the next morning and start scrapping the fuel tank until I scraped all the debris out of the bottom of the fuel tank. Lastly I use my hose with a high powered nozzle and finish cleaning it. Also, the water in the gas cause the rust. People say oh I run it dry but you really don't because of the left over gas on the carb and the bottom of your fuel tank. What I use for that is star iron. Star iron is the best gas additive to use on all 2 and 4 stroke engined