Drinking before you eat can fill you up so you have no room for the food so not a good idea early out. It makes your pouch wetter too I believe, so food can slide through quicker though I'm not sure about that. If you eat and there is no where for it to go downward, it will have to come out up wards and that is never a good thing lol
Conversely drinking right up to eating is recommended by some surgeons for those who are a year or more out. They call it water loading and it can help prevent over eating as your appetite increases and you find your able to eat larger portions.
Drinking too soon after a meal (Within 30 minutes) can wash the food out of your pouch so you feel hungrier sooner. This should be avoided obviously as it can lead to snacking as your appetite comes back with a vengeance after a few months post op.
I have read it can also cause late dumping too as it washes the food into your intestine quicker than your pouch would normally empty and you might not be able to cope with the food hitting your gut so quickly resulting in a kind of dumping
It gets harder as you are further out to maintain this 30/30 regimen, sometimes I am so thirsty after a meal I find I'm counting the minutes LOL