Are you "seasoning" your grill pan? Cast iron pans, once well seasoned, require very little cleaning. After using it, clean it -- I use hot water and a scrubby -- then oil it liberally and put it in a 400 degree oven for at least 20 or up to 30 minutes. Take it out, let it cool, put it away. Do that every time you use it and eventually, it almost cleans itself. After a while, a well-seasoned black iron skillet (or grill pan) needs only occasional seasoning. Also, are you putting any oil in it when you use it? That will also help with the cleaning.
"If you're lucky enough to live in the mountains, you're lucky enough."