can swim get by without a three neck and just use a two neck flask ..... and can swim just scale reactions DOWN so swim can just use the same'ole 1L flask instead of risking more exposure by ordering a 2L flask ........
You don't need multi-necked flasks at all for what you're trying to do but they are convienient. A 2L flask is no more "suspicious" than a 1L flask. There are many vendors you can find on the net that genuinely don't give a fuck about what you order or are trying to do.