So, I was in a hurry to get to Salem last year and I just flew with an unpainted tank.  I really want to paint my tank to match the plane while the weather has me grounded -- but it's all slimy with castor.  What's the best way to clean it?  Isopropyl alcohol?  Soap & water?  Phosphoric acid?  Lye?  All four?

Dish washing liquid soap, as stated, plus a good scrubbing with 0000 dry steel wool.  Tis will give the paint some "bite" in the metal.  Be sure to use the furniture  grade wool stuff as it will not have any oil in it.  Be sure to cap the fuel tubes
If you can find an epoxy based paint that matches the plane, all the better than using dope. Fuel will eventually dissolve the dope on the tank. The nature of the beast.

I forgot to mention that the plane is painted with Rustoleum protective enamel spray-bomb, so that's what I was planning on using.  Hopefully it'll be fuel proof with unrelenting exposure -- it's sure been OK in the area around the fuel tank, though.

It should clean up just fine.  Dawn makes a Grease Dissolver (or some such, I have some in the basement) that really does a good job of cleaning grimy engines.  I have found that using a good metal etching primer really helps the longevity of the paint job!

And that Dawn cleaner really make things rust and oxidize very badly, be sure to neutralize the part and protect it from rusting afterwards.

Randy