Cooking a large pork roast in a slow cooker

Your best bet would be a dutch oven on a low to medium low heat in the oven. You could use a regular pot in the oven, but you'd need to stir it regularly (maybe every hour) to stop everything from sticking to the sides and burning.

Properly?

You throw it in a pit with hard wood coals for at least 8 hours. Of course we don't refer to that as roasting. :)

Oven roasting is easier. Turn the oven on to 250F or so. Put something flavorful on the roast. Stick in a probe thermometer and put it in the oven.

Remove when the thermometer reads 150F. Let it rest for a few minutes before carving.

For more color and fat rendering you can roast at 450F for 10 minutes before dropping the oven to 250F and putting in the thermometer.

Flavorings are varied of course. Apple works well.