Hi Amber -- sorry to hear your daughter needed to have a tube placed. We don't use sterile water. I'm guessing they are having you do that because she's so young -- like you do for formula etc. when they are little. I'm sure they will let you switch soon.
As for the formula still being in there after so much time, no it shouldn't be that way. But honestly so quickly after surgery, her system may be seriously slowed. Alyssa struggled for two months with slow motility and high amounts of reflux post surgery....its a combinatioin of being under anesthesia, the opiates they use for pain management etc.
Is she passing stool okay? If she isn't and she isn't digesting the formula, I'd talk to the docs. If she is stooling and her stomach is just working slowly, I think I'd just give it a little more time.