The problem with soaking/washing, is that it only gets out the liquid; removing the gunk that builds up is a lot trickier.
By washing the atty out in hot water, and heating the gunk to a powder, a second wash will remove it. For example:
Wash out the existing liquid by swilling the atty around in hot water, then blowing it out by putting your mouth over the battery end. Do this a couple of times.
Give the atty a shake, and another quick blow-
through, put it on a battery and press the button until the coil glows - then let go. Give it 10 seconds to cool, then do it again; repeat this several times, I normally do this about 6-7 times.
Now press the button until the coil glows, and let go. You want to press the button again when the coil dims, and release when it's glowing. By keeping the coil glowing for about 20 seconds using this method, the gunk that's accumulated should be pretty powdered. Give the atty another hot wash and blow, then heat it up a few times to dry it out.
There is a reasonable chance of killing the atty if it gets
too hot, so go easy at first.