Tommee Tippee Advanced Anti-Colic bottles leaking

[kirby2000]

I bought a 6 pack of tommee tippee advanced anti-colic bottles and every single one of them leaks. I've watched multiple videos of putting them together incase I did it wrong but they still leak, has this happened for anyone else and does anyone have tips on how to stop it?

Thanks

Googling suggests it seems to be an issue if the milk is too hot or the valve at the bottom of the straw is not open properly

I put pumped breast milk into them so maybe it is the valve not opening. Thank you