We picked up a cast iron skillet at a yard sale a while back. It wasn't so much seasoned as never cleaned. This thing had a crust around the inside you wouldn't believe. It was a medium sized skillet with low sloping sides so we decided it had potential.
I spent about an hour with a wire brush in my angle grinder, getting it knocked down to pretty much clean metal, at least free of all organic matter. I lit all three burners on our gas grill and while it was heating up, I melted a couple of tablespoons of lard in the pan. I wiped it all around and made sure there was a little liquid in the bottom. I took it out and threw it on the grill, upside down, and let it heat the rest of the way up. When the grill seemed to hit the max temp and quit rising, I shut it off and left it cool completely.
I did this three times and the pan is slicker than cat poo on a linoleum floor. All the smoke and stink is outside and the grill doesn't care if it gets some burned lard drips in the bottom.
To clean our cast iron, we just wipe it out with a wet dish cloth and hot tap water. If it has stuck crud, we'll heat it up and pour in cold water, scrape it with a spatula like you are deglazing it to make gravy. Dump the goo outside and do the hot water and dish cloth thing.
We always dry them on the stovetop and give them a wipe with a lard brushed paper towel if they look like they need it.
Your mileage may vary, this works for us.
Tim