strange
i am under the impression there is no point in taking probiotics when you have an ileostomy as everything just passes through.
once the j pouch is activated and it becomes a 'storage' site, then its beneficial to have friendly bacteria there.
if you have gastroenteritis can't you get tested for that?
as for dehydration, when my output was very liquid after surgery i drank the st marks solution which you can make yourself at home and drink as much as you want
drinking more water will actually make you more dyhdrated.