Pouch
You won't wash the nutrients away. Nutrients aren't absorbed in your pouch, at least most aren't. They are absorbed in your small intestine. Drinking with your meals would just get the nutrients to your small intestine where they would be absorbed even faster.
The problem with drinking with meals is that it washes food out of your pouch, though, and when your pouch is empty, you'll get hungry again. So drinking with meals can make you hungry sooner and lead to eating too much.
Please note: I AM NOT A DOCTOR. If you want medical advice, talk to your doctor. Whatever I post, there is probably some surgeon or other health care provider somewhere that disagrees with me. If you want to know what your surgeon thinks, then ask him or her. Check out my blog.
I have been told 15, 30 and 45 min. But I guess it depends how you feel after eating. Once in a while I may drink a sip or two during a meal if it feels like its getting stuck but I try to at least wait 15min...if Im feeling REALLY full then I wait longer. Though there is no rule for it if you're still feeling full - go ahead and wait. And yes they don't wash away - nutrients are absorbed in the small intestine.