the insides of the bottles, the rubber part, wear out over time. do you know if you can buy replacement for that? It's the part you insert the straw in. Sterilizing in the bags must have worn them out. ?
I haven't had much luck either with the bag strerlization. I boil a pot of water and then place the parts in it I turn heat off and let sit for about 15 min. works well for me.