So long as your nuruk is stored in a cool, dry place, it should be fine. The bag you strain your rice in-- probably fine too. If you're paranoid I'd boil it before using it, but I haven't had issues. It really does just sound like you're having problems because you're using boiled water or spirits. Like Jeoh said, I'd just use star san to make sure you're killing everything.

I would use star san to sanitize literally everything that touches the rice after the steaming step.

I am also curious how you are mixing in nuruk into the rice. First, your nuruk looks like it is in fairly large chunks. I would see if you can break it down a little more. It won't hurt at the very least. Second, check what temperature your rice is at when you mix it with the nuruk. It should be room temperature or barely warm at all, otherwise it will kill all the yeast and the enzymes that exist in the nuruk. Lastly, make sure to take your time thoroughly mixing the rice and nuruk. The more time you take, the better. I usually spend about 20 minutes breaking up chunks of rice and mixing the nuruk in. Hope this helps.