My gas tank has been empty and sealed up since 05’. Any ideas on what to flush it out with?

I'd assume a petroleum based solvent or an alcohol.

I modified my cq tank recently (the diameter of the supply line at certain points just 4.3mm) and cleaned it as well.

Ive tried the vinegar/baking soda combo, its good if you have flash rust.
Mine had more deposit, not necessary rust


Than I used 2 gallons of muriatic acid, moved the tank around, for 20-30 mins each side, sun helped too, its was 74F


However if you "attach" the surface, ,you have to seal/threat it right away, otherwise flash rust thank rust will come back.
I used the POR15 tank sealer