I used to rinse, soak overnight in water (filtered, and rather highly filtered) and then would wash again the next morning, then leave to air dry (I live in a desert, a blowdryer on low can work).
I did cease the practice as a) I wasn't really sure how "clean" they were getting b) I found coil life was pretty unpredictable and once my coil went "burnt" that would result in having to discard e-liquid more frequently, so I'm not sure what the cost savings really were and c) I got into rebuildables and a lot more mods, so my coil life is a LOT better than when I split my vaping between a couple of Nautilus 2s. I still enjoy many drop in coil tanks, but I find my coil life has improved vastly with DIY and not chain vaping and I have less gunking factors now.
I still SAVE my spent coil heads (for one, the Joytech CLR coils can easily be rewicked or rebuilt, easier than some RTAs, honestly) but also my Nautilus ones in case I can't get them in the future (though I still have BUNCHES of new ones) just in case I get bored in the Vacopalypse closet and a futuristic world in which I have time on my hands to rebuild those coils (technically, I'd make the husband do it, LOL) and I feel like a bit of a hoarder over it, but I LIKE those coils and want to have them in any eventuality though I guess since I am also using RTAs I'm set in any case.
I wouldn't use soap though, I'd think that would make then taste terrible. Vodka or everclear would probably work better, although again, I'd rinse them pretty well before using them after they soak and etc.
Anna