I use one-step for all my sanitizing, but you could use the sulfite you have. Either the campden tablets or the powder. It's cheaper to use and mix up the powder. And it's no rinse.
As far as adding the campden, if you don't have an so2 meter (and I don't), you should add it every other racking at the dosage of 1 crushed campden tablet per gallon. That should keep you in the 50 ppm range. And of course at bottling. So, if you used campden in the primary, I wouldn't add it when racking to secondary- but I would the next time. I write this all down in my notes so I know when to add it. Some day I'll get a meter and then I won't have to do this!
Broken Leg Brewery
Giving beer a leg to stand on since 2006