R.D.
I like Tamara and Heather's advice.
My mother is extensively trained in early childhood development, and is recently retired from close to thirty years of working as a kind of 'child advocate,' so I trust her advice expilicitly. She warns NEVER NEVER NEVER punish a child when potty training. This could lead to resentment and hostility, among other undesirable effects. Be patient. Have him (or watch you) dump it in the toilet and flush it, then clean up, put on fresh, and go on with your day. Always have fresh pants when you are out until the problem is gone, and whatever you do, once you introduce "big boy underwear," DON'T go back to diapers. Once you make the switch, make it stick. Otherwise he could get confused, and think it doesn't matter, because diapers can always come back. You may want to consider a reward system for him. Stickers work good (gold stars on the calendar or a bright colored paper...even on the kiddy potty...) to show how well he's doing. Figure out what he likes best, and go with that!
Just remember to never use food (OR CANDY) as a reward (getting extra) or punishment (not getting something) for anything ever! This could lead to food issues as kids grow up (anorexia or obesity)!
Hope that helps!!