Paddington
Yes - your right there is apparently a major concern regarding explosive breast milk.
I have made enquiries and it would appear that one can, infact, take unlimited quantities of breast milk through security as long as it remains within said breasts.
There are no rules to say how much fluid you can take back 'out' through security in any receptacle you choose.
Just tell the Captain to get on with the crossword !
All the best.