@Naomi that makes sense thank you☺️
I use a nuby and just throw that in the milton steriliser. I try to just leave it for the recommended 15 mins but they have occasionally been in there for a few hours and are absolutely fine
I dont have the go prep but I do have the rapid cool and that also says you can cold water sterilise. I float the lid sensor side down in the solution so the bit that touches the inside of the flask is sterilised.