I have been swept 3 times and they were all different:
1) DW 2006 1st try at the marathon too slow-had no idea. There is a 16 min pacer...he passed me while I was in the potty. I was totally clue-less. The vans were at the sweep point and you got on. Very business-like attitude.
2) DL 2006 1/2 Marathon Was swept at 10 minute point by rude, uncaring, and incorrect "people" they swept me 5 minutes before the official sweep time. They called the cops on bikes if you refused to get on the bus. We spoke with the people in charge....I got "we're very sorry, but we can't put you back on the course, here's your medal"
3) DW 2007 I knew my chances of finishing the marathon were slim...my training had been poor, and i had been ill. I saw the pacer but just couldn't catch up. The sweepers were very encouraging and friendly.They allowed me time to move up so I wasn't in last place before the swept me. They kept saying the van is here any time you want to get on....but at 6.2 miles that option was taken from me.
All Three times were different. There is a 16 min pacer with balloons and flags,they are the last people to cross the finish line. Keep your eyes open. It helps that you'll be with a group so they can keep an eye out while you are taking care of business and not get suprised. I'm sure you will be fine, enjoy the "ride". I'll be cheering this year for the half and the full... my husband and son are "goofy" this year.