Never combine the cold milk with warm
breast milk, so each time you will have to store one bottle (or the
breast milk bags are good too)....once the milk is cold you can combine them. Whoa...off track, sorry! After I put the milk away I would wash the plastic nipple attachments and the other bottle. I used hot soapy water, then just set out to dry. At the end of the day you can steam everything. The tubing I would steam once a week, as no milk ever gets into that part.