Boil first then just wash after that and I would boul water then turn ot off and lace the nipples in it ever week or so. And then I tossed them out and replaced kinda often too. Medela makes sterilization bags too. i used the drop in inserts and I used the vent air too. I did buy the pricey ameda or whatever brand it was but he refused those. The best for us was the drop in playtex with the big orange nipple at first then after those the vent air. sometimes if you get lucky you can get the drop in bags on clearance too

I used both the ones with the hard ring around them that dropped in and the bags that folded over. the fold over bags are by far the cheapest route to go!
Oh and also seems like i found milk bags that I could just take straight and put into his drop in bottle....but it's been so long ago that I forget.
and one more thing LOL I'm a germ freak and you don't have to boil the nipples like I did LOL. Just washing is enough after the first initial boil