Can anyone tell me what tool is used to open the clean out valve?

Why can't it be tool-less to get in?

Any tips on snaking it out?

Any snake recommendation? I have a short line (20 feet at most).

Anyone head of Root Kill? A plumber recommended to friend when plumber
couldn't get flow problem resolved. Available at Home Cheapo. Anyone
use it?

I know it's not a root problem. It just plain gunk.