Hi All,
Caswells sell a remover that breaks down the old coating, it works well, be very careful of your paintwork

The lining can also be removed using "Nitromors! paint stripper
I have used the caswells lining stuff in a couple of tanks
All is well (so far!!)
You need to do the lining in a warm place with all the parts warm as well, this makes the "gloop" run around much easier
I like the caswells product as it can be made runny with some heat and it sets slowly giving you time to make sure the tank is coated all over
HTh
John O R