**PERK** I collect cast iron cookware and trivets!! I also use them all...love, love, love my cast iron, and won't have any teflon in the house!!
Jan is ever so right...NEVER wash with soap or an abrasive. Just hot water, and guess what? You can use a "Chore Boy" metal scrubbie on them!! :D
To season? Clean the pan, and it's the only time it's ok to use hot soapy water...if the pan is old and has a build up of old grease, spray it down with oven cleaner and seal it into a black trash bag, set it out on the porch for a few days. Wash in the hot soapy water and pop it into your oven for about 20 minutes at 250. When the pan is dry and hot, (wear your Ov-glove) spray it with Pam, inside and out, and then do your best to wipe ALL of the Pam off! (It won't happen, trust me! You want a VERY thin coating of Pam on the pan. Pop it back in that 250 - 350 degree oven for about an hour. All done...all that's left is to fry some taters in the pan...not too many, cuz you're going to all but burn them and toss them.
Rinse in hot water, stove top burner to dry, and you should be ready to cook, old fashioned non-stick style! :)