Fuel tanks - cleaning using sealers

[rendo]

Im putting my PK back on the road shortly and noticed that there is some ‘lining’ inside the tank that is flaking. I thought initially it was old due residue but I think it may have been lined before. It’s kind of like an old varnish. I intend to clean it but not sure whether I should use a tank sealer like POR15 or similar. The metal of the tank looks in very good condition, no corrosion or rust.
Some of the chemicals recommended for cleaning look quite aggressive and can contain rust inhibitors but I wonder if that’s why the sealers are required afterwards.
Any thoughts on what to clean with and should I seal it or just use it with bare metal.

[henri]

the kind of "varnish" your seeing i doubt is a sealant , its more likely old fuel an oil deposits .
you can clean it out with some fresh fuel an a handful of nuts ,shaken for ages ,an then flushed out .another way of cleaning tanks is to use full strength limescale remover ,the ones with sulfuric or phosphoric acid in .phosphoric ones better , 2 litre bottles of that,top up with warm clean water an handful of nuts . an leave for 24 hours giving a shake every now an then .it will destroy the tap in that time aswell ,empty tank an flush with clean water ,then immediately dry internally with a heat gun or blowtorch .if tanks not dried straight away it can flash rust ,especially if sulfuric is used ,phosphoric leaves a better surface .

if you decide to use a sealant like por15 , get the whole kit , cleaner ,prepper an sealant an follow the instructions to the letter ,or it wont work .H

[jbcollier]

Sulphuric acids can react violently with aluminium. Remove the tap and seal the hole with a rubber bung. Phosphoric is the way to go as it leaves the surface relatively inert.

[tzsteve]

Phossie acid all the time, 15% is all you need but you can get stronger and dilute.
Handle with care and get some plain tap water ready just incase of spills.
it takes a few hours

[rendo]

Thanks for the comments.
Ive decided to go with a tank renewal kit from rustbusters.
It comes with a cleaner to remove all the old sealer (dont think this is old fuel/oil as it is on all surfaces including the top), then a new sealer is applied.
Its not that cheap and a new tank may have been a better option.

The worry I had with the acids is what effect the have on the metal of the tank. After using acid, would you just use as normal or is there a method to protect or prime the metal.

The rustbuster kit does have enough to do other tanks which maybe handy on other scooters I have.