How to get greasy build up from inside bottles?

hi i have 6 children but i have breastfed the first five but have had to bottle feed my now 4 month old son. It seems no matter how much i scrub the inside of the bottles i cant get this greasy film from inside the bottle especialy the nipples. I have tried using the dishwasher, hand washing and then sterilising... show more hi i have 6 children but i have breastfed the first five but have had to bottle feed my now 4 month old son. It seems no matter how much i scrub the inside of the bottles i cant get this greasy film from inside the bottle especialy the nipples. I have tried using the dishwasher, hand washing and then sterilising them but no combinations seem to work. Is there a trick to it any help or sujestions would be greatly apreciated.
Update: i do use a bottle brush and they are the tommy tippee closer to nature bottles.
Update 2: i am also in australia we dont really have the bottle bags
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