I have just bought some of these bottles and the instructions suggest that they should be totally dismantled for sterilising. I am confused by this as the other bottles I have used (Avent/Tommee Tippee) can both be sterilised with the teat part assembled. Although I wash my hands before pereparing the feed, surely there's no point in sterilising the bottles etc if I am going to be fiddling about assembling them before using? Is anyone familiar with these bottles and what do they do?