I've never had any problems what so ever with modern fuels (high toluene content ) and Por 15's tank liner. In fact i even use it inside the water jackets on Ponton and W189 engines and the latest has been on the inside of a oil pan on a racer which was dinged and wouldn't stop leaking through pin holes.
As can be seen,heat doesn't affect it either.
i wouldn't ever bother with a dirty tank, because I dont' like being stranded on the side of a highway,freeway etc.