Put apple cider in crock pot OR a large pot on stove-top;
Add mulling spices in metal tea ball.
Slice orange & add.
Does not need to boil, but tastes great after @ 20 min over low heat. WILL get concentrated over a long party, so you may want to add up to another quart of cider to keep this from getting too sweet.
Add rum just before serving or directly to mugs, if party has a mixed age group. This amount is usually plenty for a 2-3 hour party, especially if coffee is another option for guests. Some folks only care for one glass of cider (sugar).