Dunking the bag in Star San is good enough. If you use a bag, your hops will float even if they are pellets (pellets usually sink after a few days, whereas whole hops will always float) unless you weigh them down with sanitized marbles or something.
(Note that it is highly debatable whether this matters, some people prefer them to sink and some people don't care what they do)
If you just throw pellets in they will sink and you can just rack away from them like a yeast cake - typically you can just avoid the them if you brewed enough beer to account for volume loss to the hops. If you used whole hops or if the pellets clog the siphon, tie the bag you were going to use to contain the hops around the inlet area of the siphon.