I have a 'vegetable' brush that I got from Williams Sonoma years ago. It's rather stiff bristled. I scrub the worst of the dirt with warm water and cook as desired. Baked; sliced/diced for home fries; cut up for mashed w/peels. Doesn't matter; don't worry about whatever dirt/spots may be left behind. If there is a dark spot within the potato as I'm cutting, I'll toss that but otherwise I don't worry about it. Have been doing this for decades and no worse for wear.