Hmm, cast iron should be pretty painless to clean. You are using an outdoor grill for parties so I'm guessing the "gunk" referred to would be something like burnt and dried up bbq sauce. If so, that's not really intended for use with cast iron. They are great pans for high, consistent heat, but don't mix well with foods that are sticky or those that burn at lower temps, sugary bbq sauces being one of the worst. Otherwise most food debris should be able to be wiped clean with a towel, and maybe just soap and water like any other dishes, but no intense scrubbing. And yes, the little bit of grease left behind after wiping with a towel is actually good for the pan. But you don't want to leave "gunk" on it.

Hope this helps..