The real problem is renewing the liner before you have rust holes.
Acetone will remove the old liner.
I have over the years used a number of tank lining products. Most have various problems, KREEM and POR hold a special place in my heart for being worthless junk
The two I use and reccomend are::
Red, White and Blue - an Australian product
www.redwhiteandblue.com.au One of the few manufacturers confident enough to put how-to videos on YouTube. It works brilliantly - full stop.
The other is RedKote, very similar to the OEM liner the requires a lot more prep than RWaB, but it does work well.