hi ! have just got Avent Microwave Steriliser down from storage ready for imminent arrival of number two any minute. did not keep instructions. I remember having to put 200ml of water in it, but can't remember how long it is supposed to go in the microwave for. can anyone remind me ? It is the round one, with blue inside base, cream/white outside base and a see-through plastic lid, takes 4 bottles, and "Avent Naturally Express" written in small-ish letters on the lid. thanks!