Identify what's in my gas tank

I cleaned out a gas tank on an old buick made in the 60's has over 350000 miles always run on leaded and regular unleaded gasoline it recently would not get fuel to pump after running for 6 months on ethanol added gasoline so I removed the tank and cleaned it out I found lot's of light brown stuff kind of a rubber substance like silicone caulk one piece was about 2.5" oblong in size by 1/8" thick like it had run to to the bottom of the tank and made a puddle there what I am wondering if this is what they call gum build up from using regular gasoline for so long and has built up on the inside of the tank and come loose from using ethanol or I have also been putting things like acetone and paint thinner also one time I put a floor cleaner solution that I later seen had wax in it any thoughts what this might be? Also if you just use regular gas and switch to ethanol based gasoline does this always mean you will have to clean tank out or will ethanol dissolve gum build up so it passes right thru fuel system or will gum never turn back into a liquid state?


John