You hear this sometimes from cast iron owners that think using some soap will "ruin" the seasoning. It's a myth, you can absolutely use soap. My preferred method is chainmail + coarse salt + small drop of dawn.
Yes, I use a little bit of Dawn when the pan is really greasy or crusty. Hot water in the pan, a little bit of Dawn, let it sit for a few minutes, scrub. Dawn is not agressive enough to remove the seasoning, it will just emulsify the liquid grease/oil in the pan.
Do not put them in the dishwasher though, or you'll have to re-season them.
Dawn kinda smells tho, especially when the pan is heated again for the first time. Whatever it pyrolyzes to, I'm not sure I want to smell or eat it. The store brand dishwasher detergent seems to not smell as much but if there's no debris from the food I avoid soap or use it very sparingly.
Good tip with the coarse salt, I'll have to try that sometime.
