Scrub your potatoes to clean them, and dry them off with a paper
towel. With a fork, poke a few holes in the potatoes. This will
allow steam to escape during the cooking process. Cut a piece of
aluminum foil large enough to thoroughly seal around the potato.
Lay the potato on the foil, sprinkle a little salt and pepper (and
a little garlic powder, if you like, and add about a teaspoon of
butter. Wrap the potato until it is completely sealed so when the
butter melts, it won't run out.
Lay the potatoes on a hot area of the grill and grill them for about an hour. Depending on their size smaller potatoes may not take as long to cook. I like to turn my potatoes a few times with a tong to allow for even cooking.
Using tongs or oven gloves, gently squeeze the potato. If it feels soft all the way through, it should be done.
Alternatively, I sometimes place the potatoes (wrapped in foil) directly around the edges of the coals. They cook on the coals while you cook other food on the grill.
You go and buy a potato, take it to your sink, run some water, get a brush and scrub the potato under the water, take it out, Lit up the grill and put the potato on and grill it until its done