Omg this is the same issue we have. I bought fairy max and a scrub mummy sponger. I wash and scrub every bit first then rinse the off. Change the sink water and do it again before the go in the Milton to be sterilised.
Also I saw someone say Milton bottle wash but I haven’t tried it to confirm
I usually rinse the bottles and add a small amount of fairy to each empty bottle I then add a tiny bit of water and scrub the bottle then rinse with hot water We are using neocate and tt bottles
Althera is horrible greasy formula, I hated it! I just used lots of washing up liquid and rinsed thoroughly! We now use Neocate so don't have this issue thankfully x
I had this issue when using pepti 1 the bottles were always greasy never felt clean I washed them and we use a Philips steam sterliser and they did come out feeling clean x