Ok its really simple, you dont have anything at the bottom of your pouch to stop food dropping through the tiny stoma your surgeon has created, therefore if you eat and drink at the same time you turn the food in your pouch into a slurry an it falls through quicker, this way you find you can eat more, and you'll find you get hungry quicker, the idea is to fill your pouch to restriction and keep the food in there digesting as long as possible, thus preventing you snacking or feeling hungry quicker.
So we dont eat during a meal, or for at least an hour and a half post meal !
Drinking before a meal........ well the juries out on that one, water loading is a good way to make the roux limb swell and means you'll find it takes less food to reach restriction, but if you drink minutes before eating your pouch will be full of fluid and you'll find you wont want the food, so i try to make sure the last drink i had was at least 15 minutes before i eat, this way i go part way towards water loading and i'm maintaining hydration.