Removing old coated lining

Urethane?

Try scrubbing with pot scrubber for Teflon pans

If you scrub it and remove all loose material, maybe you can re-coat without removing everything. Also use detergent and rinse it real good.

Sort of like painting a house

Do one and see how it turns out

What are you going to re-seal with and what do the directions say?

I've had great success removing old polyurethane coatings on nylon by just washing the items in a standard washing machine on normal settings using regular powdered detergent. Wash them by themselves as the old coating comes off in innumerable bits. Afterwards you have to run an abbreviated wash cycle in the empty washer to get rid of it all.

In the two or three cases I've done this a single wash removed all the old coating, with nothing hanging on and coming off slowly over the next decade. On the other hand, I had one tent rainfly whose coating became sticky, and no amount of washing seems to get it off. I will recoat over the old (still sticky) coating and hope for the best.

I'm not concerned about recoating, I'll use a liner. I'm throwing them in the wash when I get home, let you know how it turns out.