Tank Sealer Nightmare.

Does anybody have any ideas on removing old tank sealer from a gas tank? I've done alot of gas tanks over the years, and tried several different types. In the mid 90's I painted alot of tanks and primarily used Kreem. Then I had three of my own gas tanks sealers fail on bikes that were ridden regularly. So again I quit using sealers. A few years ago, I put a new tank on my 78 rigid, and used a different sealer. It was fine for about two years, and then I got sick and wasn't able to ride regular for about a year. I ran low on fuel and put it on reserve but it wouldn't work. It turned out that the sealer had folded down around it. I can't remember the type of sealer. It's brown in color, unlike Kreem being white. Any help would be appreciated.