You can run some acetone through it to get rid of the last bits.
If the tank isn't leaking, why bother to line it?
Every time we get a bike in the shop that has been coated (no matter what the coating), the tanks have condensation between the liner and metal that rots the crap out of the tank faster than if it were just left alone.
The act of lining a tank that is not leaking ruins more tanks than it saves.
We only use the POR15 kit when the tank is super rare AND is leaking AND we don't want to ruin original paint.
Kreem is Krap.
I have pictures of me twisting out a Kreem Krap liner from a 74 CL450 tank. The outside of this liner was LOADED with rust from the condensation that got in there. I cleaned the tank the same way I told you to (with vinegar), and since it didn't leak.... I didn't reline it. Working perfectly for three years.
And you ask my experience in this field?
Well, last year there were over 200 bikes run through our shop, mostly old Jap and Brit bikes.
This year, the number will be close to double that.
So yeah, I've seen a tank or two.