For me, when you are using a cast iron, you have to adjust your idea of clean. I think of it like a grill. You're not going to spotlessly clean your grill every time you use it. There are always going to be some carbon on there that wipes off.

Honestly, the reason why I love my cast iron is because of how lazy and rough I can be with it. I rarely clean my cast iron unless I leave oil in there for weeks or there is a ton of residue from sauce or something. I use scrap out the bottom with a metal spatula and call it a day.