This is good advice, we checked on a few different sites and with the nurse, when we first started Jaydee on cow's milk.  (He has breastmilk, cows milk & formula in his diet at the moment).

When you use any container - bottle/sippy cup/cup with milk/breastmilk/formula:
1.  Rinse it as soon as possible after the use.
2.  Thoroughly hand wash the the item, take it apart when doing so and wash each individual piece.
3.  Give the item a really good rinse in hot water.
4.  Sterilise the item appropriately - either in your steriliser, by boiling or in the dishwasher.

This may seem over the top - however, it is especially important for babies under 1year, and especially for formula, as it goes off very quickly.  It may not always be practical to sterilise immediately - especially if you are out & about using cows milk for a baby over 12months.  However we always follow steps 1-3, and make sure we sterilise everything in the evening. 

Must say that i found it before we got to that stage once, but then I have also served up milk that had just gone and it wasnt showing bad and i couldnt smell it was bad....so I dont know how that compares on the scale of gross.
Valuable lessons learnt though huh....lol
Peace
EF.x  

I use pipe cleaners to clean any straws for this reason. its not nice. And we have different cups for milk and water.

It is a horrible thing to happen isn't it........Those straws can be tricky.......good reminder regards Merle

this has happened to myself thinking the dishwasher got every thing, i now double check also i have to watch my husband as he almost gave my son some apple juice in his sippy cup that had been on the bench all day (it was a hot day) and it had gone bad i told the hubby to check things before giving them to him.

I have had this happen too so we now have different cups for juice and milk. With the milk ones I wash them up normally this when i rinse them I use a bottle brush to make sure all corners are reached.

this has happened to me. i sterolized the bottle, thinking it was clean, give it to her and just before she drank it i saw, yuck it made me dry reach.

It is disgusting, isn't it!!! I have had this happen to me before too with my son's cups that come with straws.