Nuby Rapid Cool

Cold water steriliser is your best bet. Milton tablets

The lid needs sterilising too. Milton cold water tablets is the easiest way

From the Nuby site (so the answer is yes, if using on the MAM base and not in the micro): RapidCool base: The base of your RapidCool can be sterilised using UV sterilisation, cold-water sterilisation, or steam sterilisation (note: it is not microwave-safe). RapidCool digital lid: Clean the digital lid with warm, soapy water. After cleaning, sterilise it using UV sterilisation or cold-water sterilisation.